Revert of Make SkPngCodec decode progressively. (patchset #24 id:480001 of https://codereview.chromium.org/1997703003/ )

Reason for revert:
Still breaking Google3 e.g.:

https://sponge.corp.google.com/target?id=9261d31b-34fc-4f0f-981e-f92f7c5cea2c&target=//third_party/skia/HEAD:dm#shard=1|run=1|attempt=1|page=-1

https://test.corp.google.com/ui#cl=123773095&flags=CAMQBQ==&id=OCL:123773095:BASE:123773415:1464804876959:b0ea9b1c&t=//third_party/skia/HEAD:dm

Original issue's description:
> Make SkPngCodec decode progressively.
>
> This is a step towards using SkCodec in Chromium, where progressive
> decoding is necessary.
>
> Switch from using png_read_row (which expects all the data to be
> available) to png_process_data, which uses callbacks when rows are
> available.
>
> Create a new API for SkCodec, which supports progressive decoding and
> scanline decoding. Future changes will switch the other clients off of
> startScanlineDecode and get/skip-Scanlines to the new API.
>
> Remove SkCodec::kNone_ScanlineOrder, which was only used for interlaced
> PNG images. In the new API, interlaced PNG fits kTopDown. Also remove
> updateCurrScanline(), which was only used by the old implementation for
> interlaced PNG.
>
> DMSrcSink:
> - In CodecSrc::kScanline_Mode, use the new method for scanline decoding
> for the supported formats (just PNG and PNG-in-ICO for now).
>
> fuzz.cpp:
> - Remove reference to kNone_ScanlineOrder
>
> SkCodec:
> - Add new APIs:
>     - startIncrementalDecode
>     - incrementalDecode
> - Remove kNone_SkScanlineOrder and updateCurrScanline()
>
> SkPngCodec:
> - Implement new APIs
> - Switch from sk_read_fn/png_read_row etc to png_process_data
> - Expand AutoCleanPng's role to decode the header and create the
>   SkPngCodec
> - Make the interlaced PNG decoder report how many lines were
>   initialized during an incomplete decode
> - Make initializeSwizzler return a bool instead of an SkCodec::Result
>   (It only returned kSuccess or kInvalidInput anyway)
>
> SkIcoCodec:
> - Implement the new APIs; supported for PNG in ICO
>
> SkSampledCodec:
> - Call the new method for decoding scanlines, and fall back to the old
>   method if the new version is unimplemented
> - Remove references to kNone_SkScanlineOrder
>
> tests/CodecPartial:
> - Add a test which decodes part of an image, then finishes the decode,
>   and compares it to the straightforward method
>
> tests/CodecTest:
> - Add a test which decodes all scanlines using the new method
> - Repurpose the Codec_stripes test to decode using the new method in
>   sections rather than all at once
> - In the method check(), add a parameter for whether the image supports
>   the new method of scanline decoding, and be explicit about whether an
>   image supports incomplete
> - Test incomplete PNG decodes. We should have been doing it anyway for
>   non-interlaced (except for an image that is too small - one row), but
>   the new method supports interlaced incomplete as well
> - Make test_invalid_parameters test the new method
> - Add a test to ensure that it's safe to fall back to scanline decoding without
>   rewinding
>
> BUG=skia:4211
>
> The new version was generally faster than the old version (but not significantly so).
>
> Some raw performance differences can be found at https://docs.google.com/a/google.com/spreadsheets/d/1Gis3aRCEa72qBNDRMgGDg3jD-pMgO-FXldlNF9ejo4o/
>
> Design doc can be found at https://docs.google.com/a/google.com/document/d/11Mn8-ePDKwVEMCjs3nWwSjxcSpJ_Cu8DF57KNtUmgLM/
>
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1997703003
>
> Committed: https://skia.googlesource.com/skia/+/a4b09a117d4d1ba5dda372e6a2323e653766539e
>
> Committed: https://skia.googlesource.com/skia/+/30e78c9737ff4861dc4e3fa1e4cd010680ed6965

TBR=reed@google.com,msarett@google.com,scroggo@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:4211

Review-Url: https://codereview.chromium.org/2026383002
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 755bae3..f8c9bc0 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -432,55 +432,31 @@
             break;
         }
         case kScanline_Mode: {
-            void* dst = pixels.get();
-            uint32_t height = decodeInfo.height();
-            const bool png = fPath.endsWith("png");
-            const bool ico = fPath.endsWith("ico");
-            bool useOldScanlineMethod = !png && !ico;
-            if (png || ico) {
-                if (SkCodec::kSuccess == codec->startIncrementalDecode(decodeInfo, dst,
-                        rowBytes, nullptr, colorPtr, &colorCount)) {
-                    int rowsDecoded;
-                    if (SkCodec::kIncompleteInput == codec->incrementalDecode(&rowsDecoded)) {
-                        codec->fillIncompleteImage(decodeInfo, dst, rowBytes,
-                                                   SkCodec::kNo_ZeroInitialized, height,
-                                                   rowsDecoded);
-                    }
-                } else {
-                    if (png) {
-                        // Error: PNG should support incremental decode.
-                        return "Could not start incremental decode";
-                    }
-                    // Otherwise, this is an ICO. Since incremental failed, it must contain a BMP,
-                    // which should work via startScanlineDecode
-                    useOldScanlineMethod = true;
-                }
+            if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, NULL, colorPtr,
+                                                                &colorCount)) {
+                return "Could not start scanline decoder";
             }
 
-            if (useOldScanlineMethod) {
-                if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, NULL, colorPtr,
-                                                                    &colorCount)) {
-                    return "Could not start scanline decoder";
-                }
-
-                switch (codec->getScanlineOrder()) {
-                    case SkCodec::kTopDown_SkScanlineOrder:
-                    case SkCodec::kBottomUp_SkScanlineOrder:
-                        // We do not need to check the return value.  On an incomplete
-                        // image, memory will be filled with a default value.
-                        codec->getScanlines(dst, height, rowBytes);
-                        break;
-                    case SkCodec::kOutOfOrder_SkScanlineOrder: {
-                        for (int y = 0; y < decodeInfo.height(); y++) {
-                            int dstY = codec->outputScanline(y);
-                            void* dstPtr = SkTAddOffset<void>(dst, rowBytes * dstY);
-                            // We complete the loop, even if this call begins to fail
-                            // due to an incomplete image.  This ensures any uninitialized
-                            // memory will be filled with the proper value.
-                            codec->getScanlines(dstPtr, 1, rowBytes);
-                        }
-                        break;
+            void* dst = pixels.get();
+            uint32_t height = decodeInfo.height();
+            switch (codec->getScanlineOrder()) {
+                case SkCodec::kTopDown_SkScanlineOrder:
+                case SkCodec::kBottomUp_SkScanlineOrder:
+                case SkCodec::kNone_SkScanlineOrder:
+                    // We do not need to check the return value.  On an incomplete
+                    // image, memory will be filled with a default value.
+                    codec->getScanlines(dst, height, rowBytes);
+                    break;
+                case SkCodec::kOutOfOrder_SkScanlineOrder: {
+                    for (int y = 0; y < decodeInfo.height(); y++) {
+                        int dstY = codec->outputScanline(y);
+                        void* dstPtr = SkTAddOffset<void>(dst, rowBytes * dstY);
+                        // We complete the loop, even if this call begins to fail
+                        // due to an incomplete image.  This ensures any uninitialized
+                        // memory will be filled with the proper value.
+                        codec->getScanlines(dstPtr, 1, rowBytes);
                     }
+                    break;
                 }
             }
 
diff --git a/fuzz/fuzz.cpp b/fuzz/fuzz.cpp
index ec2672e..326b942 100644
--- a/fuzz/fuzz.cpp
+++ b/fuzz/fuzz.cpp
@@ -187,6 +187,7 @@
             switch (codec->getScanlineOrder()) {
                 case SkCodec::kTopDown_SkScanlineOrder:
                 case SkCodec::kBottomUp_SkScanlineOrder:
+                case SkCodec::kNone_SkScanlineOrder:
                     // We do not need to check the return value.  On an incomplete
                     // image, memory will be filled with a default value.
                     codec->getScanlines(dst, height, rowBytes);
diff --git a/gm/factory.cpp b/gm/factory.cpp
index 1468b55..831cff0 100644
--- a/gm/factory.cpp
+++ b/gm/factory.cpp
@@ -35,8 +35,9 @@
             // bitmap is unlocked.
             SkAutoTUnref<SkDiscardableMemoryPool> pool(
                 SkDiscardableMemoryPool::Create(1));
-            SkDEPRECATED_InstallDiscardablePixelRef(SkImageGenerator::NewFromEncoded(data),
-                                                    nullptr, &fBitmap, pool);
+            SkAssertResult(SkDEPRECATED_InstallDiscardablePixelRef(
+                                                        SkImageGenerator::NewFromEncoded(data),
+                                                        nullptr, &fBitmap, pool));
         }
     }
 
diff --git a/include/codec/SkCodec.h b/include/codec/SkCodec.h
index f66eb85..50875e4 100644
--- a/include/codec/SkCodec.h
+++ b/include/codec/SkCodec.h
@@ -23,10 +23,6 @@
 class SkPngChunkReader;
 class SkSampler;
 
-namespace DM {
-class CodecSrc;
-}
-
 /**
  *  Abstraction layer directly on top of an image codec.
  */
@@ -257,8 +253,8 @@
          *  If the EncodedFormat is kWEBP_SkEncodedFormat (the only one which
          *  currently supports subsets), the top and left values must be even.
          *
-         *  In getPixels and incremental decode, we will attempt to decode the
-         *  exact rectangular subset specified by fSubset.
+         *  In getPixels, we will attempt to decode the exact rectangular
+         *  subset specified by fSubset.
          *
          *  In a scanline decode, it does not make sense to specify a subset
          *  top or subset height, since the client already controls which rows
@@ -353,67 +349,6 @@
     }
 
     /**
-     *  Prepare for an incremental decode with the specified options.
-     *
-     *  This may require a rewind.
-     *
-     *  @param dstInfo Info of the destination. If the dimensions do not match
-     *      those of getInfo, this implies a scale.
-     *  @param dst Memory to write to. Needs to be large enough to hold the subset,
-     *      if present, or the full image as described in dstInfo.
-     *  @param options Contains decoding options, including if memory is zero
-     *      initialized and whether to decode a subset.
-     *  @param ctable A pointer to a color table.  When dstInfo.colorType() is
-     *      kIndex8, this should be non-NULL and have enough storage for 256
-     *      colors.  The color table will be populated after decoding the palette.
-     *  @param ctableCount A pointer to the size of the color table.  When
-     *      dstInfo.colorType() is kIndex8, this should be non-NULL.  It will
-     *      be modified to the true size of the color table (<= 256) after
-     *      decoding the palette.
-     *  @return Enum representing success or reason for failure.
-     */
-    Result startIncrementalDecode(const SkImageInfo& dstInfo, void* dst, size_t rowBytes,
-            const SkCodec::Options*, SkPMColor* ctable, int* ctableCount);
-
-    Result startIncrementalDecode(const SkImageInfo& dstInfo, void* dst, size_t rowBytes,
-            const SkCodec::Options* options) {
-        return this->startIncrementalDecode(dstInfo, dst, rowBytes, options, nullptr, nullptr);
-    }
-
-    Result startIncrementalDecode(const SkImageInfo& dstInfo, void* dst, size_t rowBytes) {
-        return this->startIncrementalDecode(dstInfo, dst, rowBytes, nullptr, nullptr, nullptr);
-    }
-
-    /**
-     *  Start/continue the incremental decode.
-     *
-     *  Not valid to call before calling startIncrementalDecode().
-     *
-     *  After the first call, should only be called again if more data has been
-     *  provided to the source SkStream.
-     *
-     *  Unlike getPixels and getScanlines, this does not do any filling. This is
-     *  left up to the caller, since they may be skipping lines or continuing the
-     *  decode later. In the latter case, they may choose to initialize all lines
-     *  first, or only initialize the remaining lines after the first call.
-     *
-     *  @param rowsDecoded Optional output variable returning the total number of
-     *      lines initialized. Only meaningful if this method returns kIncompleteInput.
-     *      Otherwise the implementation may not set it.
-     *      Note that some implementations may have initialized this many rows, but
-     *      not necessarily finished those rows (e.g. interlaced PNG). This may be
-     *      useful for determining what rows the client needs to initialize.
-     *  @return kSuccess if all lines requested in startIncrementalDecode have
-     *      been completely decoded. kIncompleteInput otherwise.
-     */
-    Result incrementalDecode(int* rowsDecoded = nullptr) {
-        if (!fStartedIncrementalDecode) {
-            return kInvalidParameters;
-        }
-        return this->onIncrementalDecode(rowsDecoded);
-    }
-
-    /**
      * The remaining functions revolve around decoding scanlines.
      */
 
@@ -533,6 +468,17 @@
          * Interlaced gifs are an example.
          */
         kOutOfOrder_SkScanlineOrder,
+
+        /*
+         * Indicates that the entire image must be decoded in order to output
+         * any amount of scanlines.  In this case, it is a REALLY BAD IDEA to
+         * request scanlines 1-by-1 or in small chunks.  The client should
+         * determine which scanlines are needed and ask for all of them in
+         * a single call to getScanlines().
+         *
+         * Interlaced pngs are an example.
+         */
+        kNone_SkScanlineOrder,
     };
 
     /**
@@ -681,6 +627,11 @@
      */
     virtual SkScanlineOrder onGetScanlineOrder() const { return kTopDown_SkScanlineOrder; }
 
+    /**
+     *  Update the current scanline. Used by interlaced png.
+     */
+    void updateCurrScanline(int newY) { fCurrScanline = newY; }
+
     const SkImageInfo& dstInfo() const { return fDstInfo; }
 
     const SkCodec::Options& options() const { return fOptions; }
@@ -707,7 +658,6 @@
     SkImageInfo                 fDstInfo;
     SkCodec::Options            fOptions;
     int                         fCurrScanline;
-    bool                        fStartedIncrementalDecode;
 
     /**
      *  Return whether these dimensions are supported as a scale.
@@ -728,16 +678,6 @@
         return kUnimplemented;
     }
 
-    virtual Result onStartIncrementalDecode(const SkImageInfo& /*dstInfo*/, void*, size_t,
-            const SkCodec::Options&, SkPMColor*, int*) {
-        return kUnimplemented;
-    }
-
-    virtual Result onIncrementalDecode(int*) {
-        return kUnimplemented;
-    }
-
-
     virtual bool onSkipScanlines(int /*countLines*/) { return false; }
 
     virtual int onGetScanlines(void* /*dst*/, int /*countLines*/, size_t /*rowBytes*/) { return 0; }
@@ -769,7 +709,6 @@
      */
     virtual SkSampler* getSampler(bool /*createIfNecessary*/) { return nullptr; }
 
-    friend class DM::CodecSrc;  // for fillIncompleteImage
     friend class SkSampledCodec;
     friend class SkIcoCodec;
 };
diff --git a/src/codec/SkCodec.cpp b/src/codec/SkCodec.cpp
index 3c485c8..3da7f5f 100644
--- a/src/codec/SkCodec.cpp
+++ b/src/codec/SkCodec.cpp
@@ -154,20 +154,6 @@
     return this->onRewind();
 }
 
-#define CHECK_COLOR_TABLE                                   \
-    if (kIndex_8_SkColorType == info.colorType()) {         \
-        if (nullptr == ctable || nullptr == ctableCount) {  \
-            return SkCodec::kInvalidParameters;             \
-        }                                                   \
-    } else {                                                \
-        if (ctableCount) {                                  \
-            *ctableCount = 0;                               \
-        }                                                   \
-        ctableCount = nullptr;                              \
-        ctable = nullptr;                                   \
-    }
-
-
 SkCodec::Result SkCodec::getPixels(const SkImageInfo& info, void* pixels, size_t rowBytes,
                                    const Options* options, SkPMColor ctable[], int* ctableCount) {
     if (kUnknown_SkColorType == info.colorType()) {
@@ -180,7 +166,17 @@
         return kInvalidParameters;
     }
 
-    CHECK_COLOR_TABLE;
+    if (kIndex_8_SkColorType == info.colorType()) {
+        if (nullptr == ctable || nullptr == ctableCount) {
+            return kInvalidParameters;
+        }
+    } else {
+        if (ctableCount) {
+            *ctableCount = 0;
+        }
+        ctableCount = nullptr;
+        ctable = nullptr;
+    }
 
     if (!this->rewindIfNeeded()) {
         return kCouldNotRewind;
@@ -232,77 +228,22 @@
     return this->getPixels(info, pixels, rowBytes, nullptr, nullptr, nullptr);
 }
 
-SkCodec::Result SkCodec::startIncrementalDecode(const SkImageInfo& info, void* pixels,
-        size_t rowBytes, const SkCodec::Options* options, SkPMColor* ctable, int* ctableCount) {
-    fStartedIncrementalDecode = false;
-
-    if (kUnknown_SkColorType == info.colorType()) {
-        return kInvalidConversion;
-    }
-    if (nullptr == pixels) {
-        return kInvalidParameters;
-    }
-
-    // Ensure that valid color ptrs are passed in for kIndex8 color type
-    CHECK_COLOR_TABLE;
-
-    // FIXME: If the rows come after the rows of a previous incremental decode,
-    // we might be able to skip the rewind, but only the implementation knows
-    // that. (e.g. PNG will always need to rewind, since we called longjmp, but
-    // a bottom-up BMP could skip rewinding if the new rows are above the old
-    // rows.)
-    if (!this->rewindIfNeeded()) {
-        return kCouldNotRewind;
-    }
-
-    // Set options.
-    Options optsStorage;
-    if (nullptr == options) {
-        options = &optsStorage;
-    } else if (options->fSubset) {
-        SkIRect size = SkIRect::MakeSize(info.dimensions());
-        if (!size.contains(*options->fSubset)) {
-            return kInvalidParameters;
-        }
-
-        const int top = options->fSubset->top();
-        const int bottom = options->fSubset->bottom();
-        if (top < 0 || top >= info.height() || top >= bottom || bottom > info.height()) {
-            return kInvalidParameters;
-        }
-    }
-
-    if (!this->dimensionsSupported(info.dimensions())) {
-        return kInvalidScale;
-    }
-
-    fDstInfo = info;
-    fOptions = *options;
-
-    const Result result = this->onStartIncrementalDecode(info, pixels, rowBytes,
-            fOptions, ctable, ctableCount);
-    if (kSuccess == result) {
-        fStartedIncrementalDecode = true;
-    } else if (kUnimplemented == result) {
-        // FIXME: This is temporarily necessary, until we transition SkCodec
-        // implementations from scanline decoding to incremental decoding.
-        // SkAndroidCodec will first attempt to use incremental decoding, but
-        // will fall back to scanline decoding if incremental returns
-        // kUnimplemented. rewindIfNeeded(), above, set fNeedsRewind to true
-        // (after potentially rewinding), but we do not want the next call to
-        // startScanlineDecode() to do a rewind.
-        fNeedsRewind = false;
-    }
-    return result;
-}
-
-
-SkCodec::Result SkCodec::startScanlineDecode(const SkImageInfo& info,
+SkCodec::Result SkCodec::startScanlineDecode(const SkImageInfo& dstInfo,
         const SkCodec::Options* options, SkPMColor ctable[], int* ctableCount) {
     // Reset fCurrScanline in case of failure.
     fCurrScanline = -1;
     // Ensure that valid color ptrs are passed in for kIndex8 color type
-    CHECK_COLOR_TABLE;
+    if (kIndex_8_SkColorType == dstInfo.colorType()) {
+        if (nullptr == ctable || nullptr == ctableCount) {
+            return SkCodec::kInvalidParameters;
+        }
+    } else {
+        if (ctableCount) {
+            *ctableCount = 0;
+        }
+        ctableCount = nullptr;
+        ctable = nullptr;
+    }
 
     if (!this->rewindIfNeeded()) {
         return kCouldNotRewind;
@@ -313,38 +254,36 @@
     if (nullptr == options) {
         options = &optsStorage;
     } else if (options->fSubset) {
-        SkIRect size = SkIRect::MakeSize(info.dimensions());
+        SkIRect size = SkIRect::MakeSize(dstInfo.dimensions());
         if (!size.contains(*options->fSubset)) {
             return kInvalidInput;
         }
 
         // We only support subsetting in the x-dimension for scanline decoder.
         // Subsetting in the y-dimension can be accomplished using skipScanlines().
-        if (options->fSubset->top() != 0 || options->fSubset->height() != info.height()) {
+        if (options->fSubset->top() != 0 || options->fSubset->height() != dstInfo.height()) {
             return kInvalidInput;
         }
     }
 
     // FIXME: Support subsets somehow?
-    if (!this->dimensionsSupported(info.dimensions())) {
+    if (!this->dimensionsSupported(dstInfo.dimensions())) {
         return kInvalidScale;
     }
 
-    const Result result = this->onStartScanlineDecode(info, *options, ctable, ctableCount);
+    const Result result = this->onStartScanlineDecode(dstInfo, *options, ctable, ctableCount);
     if (result != SkCodec::kSuccess) {
         return result;
     }
 
     fCurrScanline = 0;
-    fDstInfo = info;
+    fDstInfo = dstInfo;
     fOptions = *options;
     return kSuccess;
 }
 
-#undef CHECK_COLOR_TABLE
-
-SkCodec::Result SkCodec::startScanlineDecode(const SkImageInfo& info) {
-    return this->startScanlineDecode(info, nullptr, nullptr, nullptr);
+SkCodec::Result SkCodec::startScanlineDecode(const SkImageInfo& dstInfo) {
+    return this->startScanlineDecode(dstInfo, nullptr, nullptr, nullptr);
 }
 
 int SkCodec::getScanlines(void* dst, int countLines, size_t rowBytes) {
@@ -392,6 +331,7 @@
 int SkCodec::onOutputScanline(int inputScanline) const {
     switch (this->getScanlineOrder()) {
         case kTopDown_SkScanlineOrder:
+        case kNone_SkScanlineOrder:
             return inputScanline;
         case kBottomUp_SkScanlineOrder:
             return this->getInfo().height() - inputScanline - 1;
@@ -425,7 +365,8 @@
     }
 
     switch (this->getScanlineOrder()) {
-        case kTopDown_SkScanlineOrder: {
+        case kTopDown_SkScanlineOrder:
+        case kNone_SkScanlineOrder: {
             const SkImageInfo fillInfo = info.makeWH(fillWidth, linesRemaining);
             fillDst = SkTAddOffset<void>(dst, linesDecoded * rowBytes);
             fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);
diff --git a/src/codec/SkGifCodec.cpp b/src/codec/SkGifCodec.cpp
index dcc25b8..75e9d63 100644
--- a/src/codec/SkGifCodec.cpp
+++ b/src/codec/SkGifCodec.cpp
@@ -520,7 +520,7 @@
 
 SkCodec::Result SkGifCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         const SkCodec::Options& opts, SkPMColor inputColorPtr[], int* inputColorCount) {
-    return this->prepareToDecode(dstInfo, inputColorPtr, inputColorCount, opts);
+    return this->prepareToDecode(dstInfo, inputColorPtr, inputColorCount, this->options());
 }
 
 void SkGifCodec::handleScanlineFrame(int count, int* rowsBeforeFrame, int* rowsInFrame) {
diff --git a/src/codec/SkIcoCodec.cpp b/src/codec/SkIcoCodec.cpp
index abcf4dc..0e81b72 100644
--- a/src/codec/SkIcoCodec.cpp
+++ b/src/codec/SkIcoCodec.cpp
@@ -186,7 +186,6 @@
     : INHERITED(width, height, info, nullptr)
     , fEmbeddedCodecs(codecs)
     , fCurrScanlineCodec(nullptr)
-    , fCurrIncrementalCodec(nullptr)
 {}
 
 /*
@@ -290,7 +289,6 @@
         result = embeddedCodec->startScanlineDecode(dstInfo, &options, colorTable, colorCount);
         if (kSuccess == result) {
             fCurrScanlineCodec = embeddedCodec;
-            fCurrIncrementalCodec = nullptr;
             return result;
         }
 
@@ -311,82 +309,13 @@
     return fCurrScanlineCodec->skipScanlines(count);
 }
 
-SkCodec::Result SkIcoCodec::onStartIncrementalDecode(const SkImageInfo& dstInfo,
-        void* pixels, size_t rowBytes, const SkCodec::Options& options,
-        SkPMColor* colorTable, int* colorCount) {
-    int index = 0;
-    while (true) {
-        index = this->chooseCodec(dstInfo.dimensions(), index);
-        if (index < 0) {
-            break;
-        }
-
-        SkCodec* embeddedCodec = fEmbeddedCodecs->operator[](index);
-        switch (embeddedCodec->startIncrementalDecode(dstInfo,
-                pixels, rowBytes, &options, colorTable, colorCount)) {
-            case kSuccess:
-                fCurrIncrementalCodec = embeddedCodec;
-                fCurrScanlineCodec = nullptr;
-                return kSuccess;
-            case kUnimplemented:
-                // FIXME: embeddedCodec is a BMP. If scanline decoding would work,
-                // return kUnimplemented so that SkSampledCodec will fall through
-                // to use the scanline decoder.
-                // Note that calling startScanlineDecode will require an extra
-                // rewind. The embedded codec has an SkMemoryStream, which is
-                // cheap to rewind, though it will do extra work re-reading the
-                // header.
-                // Also note that we pass nullptr for Options. This is because
-                // Options that are valid for incremental decoding may not be
-                // valid for scanline decoding.
-                // Once BMP supports incremental decoding this workaround can go
-                // away.
-                if (embeddedCodec->startScanlineDecode(dstInfo, nullptr,
-                        colorTable, colorCount) == kSuccess) {
-                    return kUnimplemented;
-                }
-                // Move on to the next embedded codec.
-                break;
-            default:
-                break;
-        }
-
-        index++;
-    }
-
-    SkCodecPrintf("Error: No matching candidate image in ico.\n");
-    return kInvalidScale;
-}
-
-SkCodec::Result SkIcoCodec::onIncrementalDecode(int* rowsDecoded) {
-    SkASSERT(fCurrIncrementalCodec);
-    return fCurrIncrementalCodec->incrementalDecode(rowsDecoded);
-}
-
 SkCodec::SkScanlineOrder SkIcoCodec::onGetScanlineOrder() const {
     // FIXME: This function will possibly return the wrong value if it is called
-    //        before startScanlineDecode()/startIncrementalDecode().
-    if (fCurrScanlineCodec) {
-        SkASSERT(!fCurrIncrementalCodec);
-        return fCurrScanlineCodec->getScanlineOrder();
-    }
-
-    if (fCurrIncrementalCodec) {
-        return fCurrIncrementalCodec->getScanlineOrder();
-    }
-
-    return INHERITED::onGetScanlineOrder();
+    //        before startScanlineDecode().
+    return fCurrScanlineCodec ? fCurrScanlineCodec->getScanlineOrder() :
+            INHERITED::onGetScanlineOrder();
 }
 
 SkSampler* SkIcoCodec::getSampler(bool createIfNecessary) {
-    if (fCurrScanlineCodec) {
-        SkASSERT(!fCurrIncrementalCodec);
-        return fCurrScanlineCodec->getSampler(createIfNecessary);
-    }
-
-    if (fCurrIncrementalCodec) {
-        return fCurrIncrementalCodec->getSampler(createIfNecessary);
-    }
-
-    return nullptr;
+    return fCurrScanlineCodec ? fCurrScanlineCodec->getSampler(createIfNecessary) : nullptr;
 }
diff --git a/src/codec/SkIcoCodec.h b/src/codec/SkIcoCodec.h
index a227d8c..8c56aee 100644
--- a/src/codec/SkIcoCodec.h
+++ b/src/codec/SkIcoCodec.h
@@ -54,11 +54,6 @@
 
     bool onSkipScanlines(int count) override;
 
-    Result onStartIncrementalDecode(const SkImageInfo& dstInfo, void* pixels, size_t rowBytes,
-            const SkCodec::Options&, SkPMColor*, int*) override;
-
-    Result onIncrementalDecode(int* rowsDecoded) override;
-
     SkSampler* getSampler(bool createIfNecessary) override;
 
     /*
@@ -89,13 +84,5 @@
     // SkAutoTDelete.  It will be deleted by the destructor of fEmbeddedCodecs.
     SkCodec* fCurrScanlineCodec;
 
-    // Only used by incremental decoder.  onStartIncrementalDecode() will set
-    // fCurrIncrementalCodec to one of the fEmbeddedCodecs, if it can find a
-    // codec of the appropriate size.  We will use fCurrIncrementalCodec for
-    // subsequent calls to incrementalDecode().
-    // fCurrIncrementalCodec is owned by this class, but should not be an
-    // SkAutoTDelete.  It will be deleted by the destructor of fEmbeddedCodecs.
-    SkCodec* fCurrIncrementalCodec;
-
     typedef SkCodec INHERITED;
 };
diff --git a/src/codec/SkPngCodec.cpp b/src/codec/SkPngCodec.cpp
index f648431..43d1580 100644
--- a/src/codec/SkPngCodec.cpp
+++ b/src/codec/SkPngCodec.cpp
@@ -23,22 +23,27 @@
 // Callback functions
 ///////////////////////////////////////////////////////////////////////////////
 
-// When setjmp is first called, it returns 0, meaning longjmp was not called.
-constexpr int kSetJmpOkay   = 0;
-// An error internal to libpng.
-constexpr int kPngError     = 1;
-// Passed to longjmp when we have decoded as many lines as we need.
-constexpr int kStopDecoding = 2;
-
 static void sk_error_fn(png_structp png_ptr, png_const_charp msg) {
     SkCodecPrintf("------ png error %s\n", msg);
-    longjmp(png_jmpbuf(png_ptr), kPngError);
+    longjmp(png_jmpbuf(png_ptr), 1);
 }
 
 void sk_warning_fn(png_structp, png_const_charp msg) {
     SkCodecPrintf("----- png warning %s\n", msg);
 }
 
+static void sk_read_fn(png_structp png_ptr, png_bytep data,
+                       png_size_t length) {
+    SkStream* stream = static_cast<SkStream*>(png_get_io_ptr(png_ptr));
+    const size_t bytes = stream->read(data, length);
+    if (bytes != length) {
+        // FIXME: We want to report the fact that the stream was truncated.
+        // One way to do that might be to pass a enum to longjmp so setjmp can
+        // specify the failure.
+        png_error(png_ptr, "Read Error!");
+    }
+}
+
 #ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
 static int sk_read_user_chunk(png_structp png_ptr, png_unknown_chunkp chunk) {
     SkPngChunkReader* chunkReader = (SkPngChunkReader*)png_get_user_chunk_ptr(png_ptr);
@@ -53,22 +58,9 @@
 
 class AutoCleanPng : public SkNoncopyable {
 public:
-    /*
-     *  This class does not take ownership of stream or reader, but if codecPtr
-     *  is non-NULL, and decodeBounds succeeds, it will have created a new
-     *  SkCodec (pointed to by *codecPtr) which will own/ref them, as well as
-     *  the png_ptr and info_ptr.
-     */
-    AutoCleanPng(png_structp png_ptr, SkStream* stream, SkPngChunkReader* reader,
-            SkCodec** codecPtr)
+    AutoCleanPng(png_structp png_ptr)
         : fPng_ptr(png_ptr)
-        , fInfo_ptr(nullptr)
-        , fDecodedBounds(false)
-        , fReadHeader(false)
-        , fStream(stream)
-        , fChunkReader(reader)
-        , fOutCodec(codecPtr)
-    {}
+        , fInfo_ptr(nullptr) {}
 
     ~AutoCleanPng() {
         // fInfo_ptr will never be non-nullptr unless fPng_ptr is.
@@ -83,117 +75,20 @@
         fInfo_ptr = info_ptr;
     }
 
-    /**
-     *  Reads enough of the input stream to decode the bounds.
-     *  @return false if the stream is not a valid PNG (or too short).
-     *          true if it read enough of the stream to determine the bounds.
-     *          In the latter case, the stream may have been read beyond the
-     *          point to determine the bounds, and the png_ptr will have saved
-     *          any extra data. Further, if the codecPtr supplied to the
-     *          constructor was not NULL, it will now point to a new SkCodec,
-     *          which owns (or refs, in the case of the SkPngChunkReader) the
-     *          inputs. If codecPtr was NULL, the png_ptr and info_ptr are
-     *          unowned, and it is up to the caller to destroy them.
-     */
-    bool decodeBounds();
-
-private:
-    png_structp         fPng_ptr;
-    png_infop           fInfo_ptr;
-    bool                fDecodedBounds;
-    bool                fReadHeader;
-    SkStream*           fStream;
-    SkPngChunkReader*   fChunkReader;
-    SkCodec**           fOutCodec;
-
-    /**
-     *  Supplied to libpng to call when it has read enough data to determine
-     *  bounds.
-     */
-    static void InfoCallback(png_structp png_ptr, png_infop info_ptr) {
-        // png_get_progressive_ptr returns the pointer we set on the png_ptr with
-        // png_set_progressive_read_fn
-        static_cast<AutoCleanPng*>(png_get_progressive_ptr(png_ptr))->infoCallback();
-    }
-
-    void infoCallback();
-
-    void releasePngPtrs() {
+    void release() {
         fPng_ptr = nullptr;
         fInfo_ptr = nullptr;
     }
+
+private:
+    png_structp     fPng_ptr;
+    png_infop       fInfo_ptr;
 };
 #define AutoCleanPng(...) SK_REQUIRE_LOCAL_VAR(AutoCleanPng)
 
-bool AutoCleanPng::decodeBounds() {
-    if (setjmp(png_jmpbuf(fPng_ptr))) {
-        return false;
-    }
-
-    png_set_progressive_read_fn(fPng_ptr, this, InfoCallback, nullptr, nullptr);
-
-    // Arbitrary buffer size, though note that it matches (below)
-    // SkPngCodec::processData(). FIXME: Can we better suit this to the size of
-    // the PNG header?
-    constexpr size_t kBufferSize = 4096;
-    char buffer[kBufferSize];
-
-    while (true) {
-        const size_t bytesRead = fStream->read(buffer, kBufferSize);
-        if (!bytesRead) {
-            // We have read to the end of the input without decoding bounds.
-            break;
-        }
-
-        png_process_data(fPng_ptr, fInfo_ptr, (png_bytep) buffer, bytesRead);
-        if (fReadHeader) {
-            break;
-        }
-    }
-
-    // For safety, clear the pointer to this object.
-    png_set_progressive_read_fn(fPng_ptr, nullptr, nullptr, nullptr, nullptr);
-    return fDecodedBounds;
-}
-
-void SkPngCodec::processData() {
-    switch (setjmp(png_jmpbuf(fPng_ptr))) {
-        case kPngError:
-            // There was an error. Stop processing data.
-            // FIXME: Do we need to discard png_ptr?
-            return;
-        case kStopDecoding:
-            // We decoded all the lines we want.
-            return;
-        case kSetJmpOkay:
-            // Everything is okay.
-            break;
-        default:
-            // No other values should be passed to longjmp.
-            SkASSERT(false);
-    }
-
-    // Arbitrary buffer size
-    constexpr size_t kBufferSize = 4096;
-    char buffer[kBufferSize];
-
-    while (true) {
-        const size_t bytesRead = this->stream()->read(buffer, kBufferSize);
-        png_process_data(fPng_ptr, fInfo_ptr, (png_bytep) buffer, bytesRead);
-
-        if (!bytesRead) {
-            // We have read to the end of the input. Note that we quit *after*
-            // calling png_process_data, because decodeBounds may have told
-            // libpng to save the remainder of the buffer, in which case
-            // png_process_data will process the saved buffer, though the
-            // stream has no more to read.
-            break;
-        }
-    }
-}
-
 // Note: SkColorTable claims to store SkPMColors, which is not necessarily
 // the case here.
+// TODO: If we add support for non-native swizzles, we'll need to handle that here.
 bool SkPngCodec::createColorTable(SkColorType dstColorType, bool premultiply, int* ctableCount) {
 
     int numColors;
@@ -372,254 +267,204 @@
     return nullptr;
 }
 
-class SkPngNormalDecoder : public SkPngCodec {
+static int bytes_per_pixel(int bitsPerPixel) {
+    // Note that we will have to change this implementation if we start
+    // supporting outputs from libpng that are less than 8-bits per component.
+    return bitsPerPixel / 8;
+}
+
+// Subclass of SkPngCodec which supports scanline decoding
+class SkPngScanlineDecoder : public SkPngCodec {
 public:
-    SkPngNormalDecoder(int width, int height, const SkEncodedInfo& info, SkStream* stream,
-            SkPngChunkReader* reader, png_structp png_ptr, png_infop info_ptr, int bitDepth,
+    SkPngScanlineDecoder(int width, int height, const SkEncodedInfo& info, SkStream* stream,
+            SkPngChunkReader* chunkReader, png_structp png_ptr, png_infop info_ptr, int bitDepth,
             sk_sp<SkColorSpace> colorSpace)
-        : INHERITED(width, height, info, stream, reader, png_ptr, info_ptr, bitDepth,
-                std::move(colorSpace))
-        , fLinesDecoded(0)
-        , fDst(nullptr)
-        , fRowBytes(0)
-        , fFirstRow(0)
-        , fLastRow(0)
+        : INHERITED(width, height, info, stream, chunkReader, png_ptr, info_ptr, bitDepth, 1,
+                    colorSpace)
+        , fSrcRow(nullptr)
     {}
 
-    static void AllRowsCallback(png_structp png_ptr, png_bytep row, png_uint_32 rowNum, int /*pass*/) {
-        GetDecoder(png_ptr)->allRowsCallback(row, rowNum);
+    Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
+            SkPMColor ctable[], int* ctableCount) override {
+        if (!conversion_possible(dstInfo, this->getInfo())) {
+            return kInvalidConversion;
+        }
+
+        const Result result = this->initializeSwizzler(dstInfo, options, ctable,
+                                                       ctableCount);
+        if (result != kSuccess) {
+            return result;
+        }
+
+        fStorage.reset(this->getInfo().width() *
+                (bytes_per_pixel(this->getEncodedInfo().bitsPerPixel())));
+        fSrcRow = fStorage.get();
+
+        return kSuccess;
     }
 
-    static void RowCallback(png_structp png_ptr, png_bytep row, png_uint_32 rowNum, int /*pass*/) {
-        GetDecoder(png_ptr)->rowCallback(row, rowNum);
+    int onGetScanlines(void* dst, int count, size_t rowBytes) override {
+        // Assume that an error in libpng indicates an incomplete input.
+        int row = 0;
+        if (setjmp(png_jmpbuf(this->png_ptr()))) {
+            SkCodecPrintf("setjmp long jump!\n");
+            return row;
+        }
+
+        void* dstRow = dst;
+        for (; row < count; row++) {
+            png_read_row(this->png_ptr(), fSrcRow, nullptr);
+            this->swizzler()->swizzle(dstRow, fSrcRow);
+            dstRow = SkTAddOffset<void>(dstRow, rowBytes);
+        }
+
+        return row;
     }
+
+    bool onSkipScanlines(int count) override {
+        // Assume that an error in libpng indicates an incomplete input.
+        if (setjmp(png_jmpbuf(this->png_ptr()))) {
+            SkCodecPrintf("setjmp long jump!\n");
+            return false;
+        }
+
+        for (int row = 0; row < count; row++) {
+            png_read_row(this->png_ptr(), fSrcRow, nullptr);
+        }
+        return true;
+    }
+
 private:
-    int                         fLinesDecoded; // FIXME: Move to baseclass?
-    void*                       fDst;
-    size_t                      fRowBytes;
-
-    // Variables for partial decode
-    int                         fFirstRow;  // FIXME: Move to baseclass?
-    int                         fLastRow;
+    SkAutoTMalloc<uint8_t>      fStorage;
+    uint8_t*                    fSrcRow;
 
     typedef SkPngCodec INHERITED;
-
-    static SkPngNormalDecoder* GetDecoder(png_structp png_ptr) {
-        return static_cast<SkPngNormalDecoder*>(png_get_progressive_ptr(png_ptr));
-    }
-
-    Result decodeAllRows(void* dst, size_t rowBytes, int* rowsDecoded) override {
-        const int height = this->getInfo().height();
-        png_set_progressive_read_fn(this->png_ptr(), this, nullptr, AllRowsCallback, nullptr);
-        fDst = dst;
-        fRowBytes = rowBytes;
-
-        fLinesDecoded = 0;
-
-        this->processData();
-
-        if (fLinesDecoded == height) {
-            return SkCodec::kSuccess;
-        }
-
-        if (rowsDecoded) {
-            *rowsDecoded = fLinesDecoded;
-        }
-
-        return SkCodec::kIncompleteInput;
-    }
-
-    void allRowsCallback(png_bytep row, int rowNum) {
-        SkASSERT(rowNum - fFirstRow == fLinesDecoded);
-        fLinesDecoded++;
-        this->swizzler()->swizzle(fDst, row);
-        fDst = SkTAddOffset<void>(fDst, fRowBytes);
-    }
-
-    void setRange(int firstRow, int lastRow, void* dst, size_t rowBytes) override {
-        png_set_progressive_read_fn(this->png_ptr(), this, nullptr, RowCallback, nullptr);
-        fFirstRow = firstRow;
-        fLastRow = lastRow;
-        fDst = dst;
-        fRowBytes = rowBytes;
-        fLinesDecoded = 0;
-    }
-
-    SkCodec::Result decode(int* rowsDecoded) override {
-        this->processData();
-
-        if (fLinesDecoded == fLastRow - fFirstRow + 1) {
-            return SkCodec::kSuccess;
-        }
-
-        if (rowsDecoded) {
-            *rowsDecoded = fLinesDecoded;
-        }
-
-        return SkCodec::kIncompleteInput;
-    }
-
-    void rowCallback(png_bytep row, int rowNum) {
-        if (rowNum < fFirstRow) {
-            // Ignore this row.
-            return;
-        }
-
-        SkASSERT(rowNum <= fLastRow);
-
-        if (this->swizzler()->rowNeeded(fLinesDecoded)) {
-            this->swizzler()->swizzle(fDst, row);
-            fDst = SkTAddOffset<void>(fDst, fRowBytes);
-        }
-
-        fLinesDecoded++;
-
-        if (rowNum == fLastRow) {
-            // Fake error to stop decoding scanlines.
-            longjmp(png_jmpbuf(this->png_ptr()), kStopDecoding);
-        }
-    }
 };
 
-class SkPngInterlacedDecoder : public SkPngCodec {
-public:
-    SkPngInterlacedDecoder(int width, int height, const SkEncodedInfo& info, SkStream* stream,
-            SkPngChunkReader* reader, png_structp png_ptr, png_infop info_ptr, int bitDepth,
-            sk_sp<SkColorSpace> colorSpace, int numberPasses)
-        : INHERITED(width, height, info, stream, reader, png_ptr, info_ptr, bitDepth,
-                std::move(colorSpace))
-        , fNumberPasses(numberPasses)
-        , fFirstRow(0)
-        , fLastRow(0)
-        , fLinesDecoded(0)
-        , fInterlacedComplete(false)
-        , fPng_rowbytes(0)
-    {}
 
-    static void InterlacedRowCallback(png_structp png_ptr, png_bytep row, png_uint_32 rowNum, int pass) {
-        auto decoder = static_cast<SkPngInterlacedDecoder*>(png_get_progressive_ptr(png_ptr));
-        decoder->interlacedRowCallback(row, rowNum, pass);
+class SkPngInterlacedScanlineDecoder : public SkPngCodec {
+public:
+    SkPngInterlacedScanlineDecoder(int width, int height, const SkEncodedInfo& info,
+            SkStream* stream, SkPngChunkReader* chunkReader, png_structp png_ptr,
+            png_infop info_ptr, int bitDepth, int numberPasses, sk_sp<SkColorSpace> colorSpace)
+        : INHERITED(width, height, info, stream, chunkReader, png_ptr, info_ptr, bitDepth,
+                    numberPasses, colorSpace)
+        , fHeight(-1)
+        , fCanSkipRewind(false)
+    {
+        SkASSERT(numberPasses != 1);
+    }
+
+    Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
+            SkPMColor ctable[], int* ctableCount) override {
+        if (!conversion_possible(dstInfo, this->getInfo())) {
+            return kInvalidConversion;
+        }
+
+        const Result result = this->initializeSwizzler(dstInfo, options, ctable,
+                                                       ctableCount);
+        if (result != kSuccess) {
+            return result;
+        }
+
+        fHeight = dstInfo.height();
+        // FIXME: This need not be called on a second call to onStartScanlineDecode.
+        fSrcRowBytes = this->getInfo().width() *
+                (bytes_per_pixel(this->getEncodedInfo().bitsPerPixel()));
+        fGarbageRow.reset(fSrcRowBytes);
+        fGarbageRowPtr = static_cast<uint8_t*>(fGarbageRow.get());
+        fCanSkipRewind = true;
+
+        return SkCodec::kSuccess;
+    }
+
+    int onGetScanlines(void* dst, int count, size_t dstRowBytes) override {
+        // rewind stream if have previously called onGetScanlines,
+        // since we need entire progressive image to get scanlines
+        if (fCanSkipRewind) {
+            // We already rewound in onStartScanlineDecode, so there is no reason to rewind.
+            // Next time onGetScanlines is called, we will need to rewind.
+            fCanSkipRewind = false;
+        } else {
+            // rewindIfNeeded resets fCurrScanline, since it assumes that start
+            // needs to be called again before scanline decoding. PNG scanline
+            // decoding is the exception, since it needs to rewind between
+            // calls to getScanlines. Keep track of fCurrScanline, to undo the
+            // reset.
+            const int currScanline = this->nextScanline();
+            // This method would never be called if currScanline is -1
+            SkASSERT(currScanline != -1);
+
+            if (!this->rewindIfNeeded()) {
+                return kCouldNotRewind;
+            }
+            this->updateCurrScanline(currScanline);
+        }
+
+        if (setjmp(png_jmpbuf(this->png_ptr()))) {
+            SkCodecPrintf("setjmp long jump!\n");
+            // FIXME (msarett): Returning 0 is pessimistic.  If we can complete a single pass,
+            // we may be able to report that all of the memory has been initialized.  Even if we
+            // fail on the first pass, we can still report than some scanlines are initialized.
+            return 0;
+        }
+        SkAutoTMalloc<uint8_t> storage(count * fSrcRowBytes);
+        uint8_t* storagePtr = storage.get();
+        uint8_t* srcRow;
+        const int startRow = this->nextScanline();
+        for (int i = 0; i < this->numberPasses(); i++) {
+            // read rows we planned to skip into garbage row
+            for (int y = 0; y < startRow; y++){
+                png_read_row(this->png_ptr(), fGarbageRowPtr, nullptr);
+            }
+            // read rows we care about into buffer
+            srcRow = storagePtr;
+            for (int y = 0; y < count; y++) {
+                png_read_row(this->png_ptr(), srcRow, nullptr);
+                srcRow += fSrcRowBytes;
+            }
+            // read rows we don't want into garbage buffer
+            for (int y = 0; y < fHeight - startRow - count; y++) {
+                png_read_row(this->png_ptr(), fGarbageRowPtr, nullptr);
+            }
+        }
+        //swizzle the rows we care about
+        srcRow = storagePtr;
+        void* dstRow = dst;
+        for (int y = 0; y < count; y++) {
+            this->swizzler()->swizzle(dstRow, srcRow);
+            dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
+            srcRow += fSrcRowBytes;
+        }
+
+        return count;
+    }
+
+    bool onSkipScanlines(int count) override {
+        // The non-virtual version will update fCurrScanline.
+        return true;
+    }
+
+    SkScanlineOrder onGetScanlineOrder() const override {
+        return kNone_SkScanlineOrder;
     }
 
 private:
-    const int               fNumberPasses;
-    int                     fFirstRow;
-    int                     fLastRow;
-    void*                   fDst;
-    size_t                  fRowBytes;
-    int                     fLinesDecoded;
-    bool                    fInterlacedComplete;
-    size_t                  fPng_rowbytes;
-    SkAutoTMalloc<png_byte> fInterlaceBuffer;
+    int                         fHeight;
+    size_t                      fSrcRowBytes;
+    SkAutoMalloc                fGarbageRow;
+    uint8_t*                    fGarbageRowPtr;
+    // FIXME: This imitates behavior in SkCodec::rewindIfNeeded. That function
+    // is called whenever some action is taken that reads the stream and
+    // therefore the next call will require a rewind. So it modifies a boolean
+    // to note that the *next* time it is called a rewind is needed.
+    // SkPngInterlacedScanlineDecoder has an extra wrinkle - calling
+    // onStartScanlineDecode followed by onGetScanlines does *not* require a
+    // rewind. Since rewindIfNeeded does not have this flexibility, we need to
+    // add another layer.
+    bool                        fCanSkipRewind;
 
     typedef SkPngCodec INHERITED;
-
-    // FIXME: Currently sharing interlaced callback for all rows and subset. It's not
-    // as expensive as the subset version of non-interlaced, but it still does extra
-    // work.
-    void interlacedRowCallback(png_bytep row, int rowNum, int pass) {
-        if (rowNum < fFirstRow || rowNum > fLastRow) {
-            // Ignore this row
-            return;
-        }
-
-        png_bytep oldRow = fInterlaceBuffer.get() + (rowNum - fFirstRow) * fPng_rowbytes;
-        png_progressive_combine_row(this->png_ptr(), oldRow, row);
-
-        if (0 == pass) {
-            // The first pass initializes all rows.
-            SkASSERT(row);
-            SkASSERT(fLinesDecoded == rowNum - fFirstRow);
-            fLinesDecoded++;
-        } else {
-            SkASSERT(fLinesDecoded == fLastRow - fFirstRow + 1);
-            if (fNumberPasses - 1 == pass && rowNum == fLastRow) {
-                // Last pass, and we have read all of the rows we care about. Note that
-                // we do not care about reading anything beyond the end of the image (or
-                // beyond the last scanline requested).
-                fInterlacedComplete = true;
-                // Fake error to stop decoding scanlines.
-                longjmp(png_jmpbuf(this->png_ptr()), kStopDecoding);
-            }
-        }
-    }
-
-    SkCodec::Result decodeAllRows(void* dst, size_t rowBytes, int* rowsDecoded) override {
-        const int height = this->getInfo().height();
-        this->setUpInterlaceBuffer(height);
-        png_set_progressive_read_fn(this->png_ptr(), this, nullptr, InterlacedRowCallback, nullptr);
-
-        fFirstRow = 0;
-        fLastRow = height - 1;
-        fLinesDecoded = 0;
-
-        this->processData();
-
-        png_bytep srcRow = fInterlaceBuffer.get();
-        // FIXME: When resuming, this may rewrite rows that did not change.
-        for (int rowNum = 0; rowNum < fLinesDecoded; rowNum++) {
-            this->swizzler()->swizzle(dst, srcRow);
-            dst = SkTAddOffset<void>(dst, rowBytes);
-            srcRow = SkTAddOffset<png_byte>(srcRow, fPng_rowbytes);
-        }
-        if (fInterlacedComplete) {
-            return SkCodec::kSuccess;
-        }
-
-        if (rowsDecoded) {
-            *rowsDecoded = fLinesDecoded;
-        }
-
-        return SkCodec::kIncompleteInput;
-    }
-
-    void setRange(int firstRow, int lastRow, void* dst, size_t rowBytes) override {
-        // FIXME: We could skip rows in the interlace buffer that we won't put in the output.
-        this->setUpInterlaceBuffer(lastRow - firstRow + 1);
-        png_set_progressive_read_fn(this->png_ptr(), this, nullptr, InterlacedRowCallback, nullptr);
-        fFirstRow = firstRow;
-        fLastRow = lastRow;
-        fDst = dst;
-        fRowBytes = rowBytes;
-        fLinesDecoded = 0;
-    }
-
-    SkCodec::Result decode(int* rowsDecoded) override {
-        this->processData();
-
-        // Now call the callback on all the rows that were decoded.
-        if (!fLinesDecoded) {
-            return SkCodec::kIncompleteInput;
-        }
-        const int lastRow = fLinesDecoded + fFirstRow - 1;
-        SkASSERT(lastRow <= fLastRow);
-
-        // FIXME: For resuming interlace, we may swizzle a row that hasn't changed. But it
-        // may be too tricky/expensive to handle that correctly.
-        png_bytep srcRow = fInterlaceBuffer.get();
-        const int sampleY = this->swizzler()->sampleY();
-        void* dst = fDst;
-        for (int rowNum = fFirstRow; rowNum <= lastRow; rowNum += sampleY) {
-            this->swizzler()->swizzle(dst, srcRow);
-            dst = SkTAddOffset<void>(dst, fRowBytes);
-            srcRow = SkTAddOffset<png_byte>(srcRow, fPng_rowbytes * sampleY);
-        }
-
-        if (fInterlacedComplete) {
-            return SkCodec::kSuccess;
-        }
-
-        if (rowsDecoded) {
-            *rowsDecoded = fLinesDecoded;
-        }
-        return SkCodec::kIncompleteInput;
-    }
-
-    void setUpInterlaceBuffer(int height) {
-        fPng_rowbytes = png_get_rowbytes(this->png_ptr(), this->info_ptr());
-        fInterlaceBuffer.reset(fPng_rowbytes * height);
-        fInterlacedComplete = false;
-    }
 };
 
 // Reads the header and initializes the output fields, if not NULL.
@@ -647,7 +492,7 @@
         return false;
     }
 
-    AutoCleanPng autoClean(png_ptr, stream, chunkReader, outCodec);
+    AutoCleanPng autoClean(png_ptr);
 
     png_infop info_ptr = png_create_info_struct(png_ptr);
     if (info_ptr == nullptr) {
@@ -662,6 +507,8 @@
         return false;
     }
 
+    png_set_read_fn(png_ptr, static_cast<void*>(stream), sk_read_fn);
+
 #ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
     // Hookup our chunkReader so we can see any user-chunks the caller may be interested in.
     // This needs to be installed before we read the png header.  Android may store ninepatch
@@ -672,31 +519,12 @@
     }
 #endif
 
-    const bool decodedBounds = autoClean.decodeBounds();
-
-    if (!decodedBounds) {
-        return false;
-    }
-
-    // On success, decodeBounds releases ownership of png_ptr and info_ptr.
-    if (png_ptrp) {
-        *png_ptrp = png_ptr;
-    }
-    if (info_ptrp) {
-        *info_ptrp = info_ptr;
-    }
-
-    // decodeBounds takes care of setting outCodec
-    if (outCodec) {
-        SkASSERT(*outCodec);
-    }
-    return true;
-}
-
-void AutoCleanPng::infoCallback() {
+    // The call to png_read_info() gives us all of the information from the
+    // PNG file before the first IDAT (image data chunk).
+    png_read_info(png_ptr, info_ptr);
     png_uint_32 origWidth, origHeight;
     int bitDepth, encodedColorType;
-    png_get_IHDR(fPng_ptr, fInfo_ptr, &origWidth, &origHeight, &bitDepth,
+    png_get_IHDR(png_ptr, info_ptr, &origWidth, &origHeight, &bitDepth,
                  &encodedColorType, nullptr, nullptr, nullptr);
 
     // Tell libpng to strip 16 bit/color files down to 8 bits/color.
@@ -704,7 +532,7 @@
     //       RAW decodes?
     if (bitDepth == 16) {
         SkASSERT(PNG_COLOR_TYPE_PALETTE != encodedColorType);
-        png_set_strip_16(fPng_ptr);
+        png_set_strip_16(png_ptr);
     }
 
     // Now determine the default colorType and alphaType and set the required transforms.
@@ -718,18 +546,18 @@
             // byte into separate bytes (useful for paletted and grayscale images).
             if (bitDepth < 8) {
                 // TODO: Should we use SkSwizzler here?
-                png_set_packing(fPng_ptr);
+                png_set_packing(png_ptr);
             }
 
             color = SkEncodedInfo::kPalette_Color;
             // Set the alpha depending on if a transparency chunk exists.
-            alpha = png_get_valid(fPng_ptr, fInfo_ptr, PNG_INFO_tRNS) ?
+            alpha = png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS) ?
                     SkEncodedInfo::kUnpremul_Alpha : SkEncodedInfo::kOpaque_Alpha;
             break;
         case PNG_COLOR_TYPE_RGB:
-            if (png_get_valid(fPng_ptr, fInfo_ptr, PNG_INFO_tRNS)) {
+            if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
                 // Convert to RGBA if transparency chunk exists.
-                png_set_tRNS_to_alpha(fPng_ptr);
+                png_set_tRNS_to_alpha(png_ptr);
                 color = SkEncodedInfo::kRGBA_Color;
                 alpha = SkEncodedInfo::kBinary_Alpha;
             } else {
@@ -741,11 +569,11 @@
             // Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel.
             if (bitDepth < 8) {
                 // TODO: Should we use SkSwizzler here?
-                png_set_expand_gray_1_2_4_to_8(fPng_ptr);
+                png_set_expand_gray_1_2_4_to_8(png_ptr);
             }
 
-            if (png_get_valid(fPng_ptr, fInfo_ptr, PNG_INFO_tRNS)) {
-                png_set_tRNS_to_alpha(fPng_ptr);
+            if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
+                png_set_tRNS_to_alpha(png_ptr);
                 color = SkEncodedInfo::kGrayAlpha_Color;
                 alpha = SkEncodedInfo::kBinary_Alpha;
             } else {
@@ -768,55 +596,45 @@
             alpha = SkEncodedInfo::kUnpremul_Alpha;
     }
 
-    const int numberPasses = png_set_interlace_handling(fPng_ptr);
+    int numberPasses = png_set_interlace_handling(png_ptr);
 
-    fReadHeader = true;
-#if PNG_LIBPNG_VER_MAJOR > 1 || (PNG_LIBPNG_VER_MAJOR == 1 && PNG_LIBPNG_VER_MINOR >= 5)
-    // 1 tells libpng to save any extra data. We may be able to be more efficient by saving
-    // it ourselves.
-    png_process_data_pause(fPng_ptr, 1);
-    fDecodedBounds = true;
-#else
-    // We may have read more than the header. Empty buffer and move to the end of the
-    // header so future calls can read the rows.
-    fDecodedBounds = fStream->move(-fPng_ptr->buffer_size);
-    fPng_ptr->buffer_size = 0;
-    if (!fDecodedBounds) {
-        // Stream could not be moved to the correct place.
-        return;
+    autoClean.release();
+    if (png_ptrp) {
+        *png_ptrp = png_ptr;
     }
-#endif
-    if (fOutCodec) {
-        SkASSERT(nullptr == *fOutCodec);
-        sk_sp<SkColorSpace> colorSpace = read_color_space(fPng_ptr, fInfo_ptr);
+    if (info_ptrp) {
+        *info_ptrp = info_ptr;
+    }
+
+    if (outCodec) {
+        sk_sp<SkColorSpace> colorSpace = read_color_space(png_ptr, info_ptr);
         if (!colorSpace) {
             // Treat unmarked pngs as sRGB.
             colorSpace = SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named);
         }
+
         SkEncodedInfo info = SkEncodedInfo::Make(color, alpha, 8);
+
         if (1 == numberPasses) {
-            *fOutCodec = new SkPngNormalDecoder(origWidth, origHeight, info, fStream,
-                    fChunkReader, fPng_ptr, fInfo_ptr, bitDepth, std::move(colorSpace));
+            *outCodec = new SkPngScanlineDecoder(origWidth, origHeight, info, stream,
+                    chunkReader, png_ptr, info_ptr, bitDepth, colorSpace);
         } else {
-            *fOutCodec = new SkPngInterlacedDecoder(origWidth, origHeight, info, fStream,
-                    fChunkReader, fPng_ptr, fInfo_ptr, bitDepth, std::move(colorSpace),
-                    numberPasses);
+            *outCodec = new SkPngInterlacedScanlineDecoder(origWidth, origHeight, info, stream,
+                    chunkReader, png_ptr, info_ptr, bitDepth, numberPasses, colorSpace);
         }
     }
 
-
-    // Release the pointers, which are now owned by the codec or the caller is expected to
-    // take ownership.
-    this->releasePngPtrs();
+    return true;
 }
 
 SkPngCodec::SkPngCodec(int width, int height, const SkEncodedInfo& info, SkStream* stream,
                        SkPngChunkReader* chunkReader, png_structp png_ptr, png_infop info_ptr,
-                       int bitDepth, sk_sp<SkColorSpace> colorSpace)
+                       int bitDepth, int numberPasses, sk_sp<SkColorSpace> colorSpace)
     : INHERITED(width, height, info, stream, colorSpace)
     , fPngChunkReader(SkSafeRef(chunkReader))
     , fPng_ptr(png_ptr)
     , fInfo_ptr(info_ptr)
+    , fNumberPasses(numberPasses)
     , fBitDepth(bitDepth)
 {}
 
@@ -838,19 +656,22 @@
 // Getting the pixels
 ///////////////////////////////////////////////////////////////////////////////
 
-bool SkPngCodec::initializeSwizzler(const SkImageInfo& requestedInfo,
-                                    const Options& options,
-                                    SkPMColor ctable[],
-                                    int* ctableCount) {
+SkCodec::Result SkPngCodec::initializeSwizzler(const SkImageInfo& requestedInfo,
+                                               const Options& options,
+                                               SkPMColor ctable[],
+                                               int* ctableCount) {
+    // FIXME: Could we use the return value of setjmp to specify the type of
+    // error?
     if (setjmp(png_jmpbuf(fPng_ptr))) {
-        return false;
+        SkCodecPrintf("setjmp long jump!\n");
+        return kInvalidInput;
     }
     png_read_update_info(fPng_ptr, fInfo_ptr);
 
     if (SkEncodedInfo::kPalette_Color == this->getEncodedInfo().color()) {
         if (!this->createColorTable(requestedInfo.colorType(),
                 kPremul_SkAlphaType == requestedInfo.alphaType(), ctableCount)) {
-            return false;
+            return kInvalidInput;
         }
     }
 
@@ -863,7 +684,7 @@
             options));
     SkASSERT(fSwizzler);
 
-    return true;
+    return kSuccess;
 }
 
 
@@ -899,38 +720,77 @@
     }
 
     // Note that ctable and ctableCount may be modified if there is a color table
-    if (!this->initializeSwizzler(requestedInfo, options, ctable, ctableCount)) {
-        return kInvalidInput;   // or parameters?
+    const Result result = this->initializeSwizzler(requestedInfo, options, ctable, ctableCount);
+    if (result != kSuccess) {
+        return result;
     }
 
-    return this->decodeAllRows(dst, dstRowBytes, rowsDecoded);
-}
+    const int width = requestedInfo.width();
+    const int height = requestedInfo.height();
+    const int bpp = bytes_per_pixel(this->getEncodedInfo().bitsPerPixel());
+    const size_t srcRowBytes = width * bpp;
 
-SkCodec::Result SkPngCodec::onStartIncrementalDecode(const SkImageInfo& dstInfo,
-        void* dst, size_t rowBytes, const SkCodec::Options& options,
-        SkPMColor* ctable, int* ctableCount) {
-    if (!conversion_possible(dstInfo, this->getInfo())) {
-        return kInvalidConversion;
+    // FIXME: Could we use the return value of setjmp to specify the type of
+    // error?
+    int row = 0;
+    // This must be declared above the call to setjmp to avoid memory leaks on incomplete images.
+    SkAutoTMalloc<uint8_t> storage;
+    if (setjmp(png_jmpbuf(fPng_ptr))) {
+        // Assume that any error that occurs while reading rows is caused by an incomplete input.
+        if (fNumberPasses > 1) {
+            // FIXME (msarett): Handle incomplete interlaced pngs.
+            return (row == height) ? kSuccess : kInvalidInput;
+        }
+        // FIXME: We do a poor job on incomplete pngs compared to other decoders (ex: Chromium,
+        // Ubuntu Image Viewer).  This is because we use the default buffer size in libpng (8192
+        // bytes), and if we can't fill the buffer, we immediately fail.
+        // For example, if we try to read 8192 bytes, and the image (incorrectly) only contains
+        // half that, which may have been enough to contain a non-zero number of lines, we fail
+        // when we could have decoded a few more lines and then failed.
+        // The read function that we provide for libpng has no way of indicating that we have
+        // made a partial read.
+        // Making our buffer size smaller improves our incomplete decodes, but what impact does
+        // it have on regular decode performance?  Should we investigate using a different API
+        // instead of png_read_row?  Chromium uses png_process_data.
+        *rowsDecoded = row;
+        return (row == height) ? kSuccess : kIncompleteInput;
     }
 
-    if (!this->initializeSwizzler(dstInfo, options, ctable, ctableCount)) {
-        return kInvalidInput;
-    }
+    // FIXME: We could split these out based on subclass.
+    void* dstRow = dst;
+    if (fNumberPasses > 1) {
+        storage.reset(height * srcRowBytes);
+        uint8_t* const base = storage.get();
 
-    int firstRow, lastRow;
-    if (options.fSubset) {
-        firstRow = options.fSubset->top();
-        lastRow = options.fSubset->bottom() - 1;
+        for (int i = 0; i < fNumberPasses; i++) {
+            uint8_t* srcRow = base;
+            for (int y = 0; y < height; y++) {
+                png_read_row(fPng_ptr, srcRow, nullptr);
+                srcRow += srcRowBytes;
+            }
+        }
+
+        // Now swizzle it.
+        uint8_t* srcRow = base;
+        for (; row < height; row++) {
+            fSwizzler->swizzle(dstRow, srcRow);
+            dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
+            srcRow += srcRowBytes;
+        }
     } else {
-        firstRow = 0;
-        lastRow = dstInfo.height() - 1;
+        storage.reset(srcRowBytes);
+        uint8_t* srcRow = storage.get();
+        for (; row < height; row++) {
+            png_read_row(fPng_ptr, srcRow, nullptr);
+            fSwizzler->swizzle(dstRow, srcRow);
+            dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
+        }
     }
-    this->setRange(firstRow, lastRow, dst, rowBytes);
-    return kSuccess;
-}
 
-SkCodec::Result SkPngCodec::onIncrementalDecode(int* rowsDecoded) {
-    return this->decode(rowsDecoded);
+    // read rest of file, and get additional comment and time chunks in info_ptr
+    png_read_end(fPng_ptr, fInfo_ptr);
+
+    return kSuccess;
 }
 
 uint32_t SkPngCodec::onGetFillValue(SkColorType colorType) const {
@@ -944,7 +804,7 @@
 SkCodec* SkPngCodec::NewFromStream(SkStream* stream, SkPngChunkReader* chunkReader) {
     SkAutoTDelete<SkStream> streamDeleter(stream);
 
-    SkCodec* outCodec = nullptr;
+    SkCodec* outCodec;
     if (read_header(stream, chunkReader, &outCodec, nullptr, nullptr)) {
         // Codec has taken ownership of the stream.
         SkASSERT(outCodec);
diff --git a/src/codec/SkPngCodec.h b/src/codec/SkPngCodec.h
index 51d8978..0a88783 100644
--- a/src/codec/SkPngCodec.h
+++ b/src/codec/SkPngCodec.h
@@ -27,9 +27,6 @@
     virtual ~SkPngCodec();
 
 protected:
-    SkPngCodec(int width, int height, const SkEncodedInfo&, SkStream*, SkPngChunkReader*,
-            png_structp, png_infop, int bitDepth, sk_sp<SkColorSpace>);
-
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*, int*)
             override;
     SkEncodedFormat onGetEncodedFormat() const override { return kPNG_SkEncodedFormat; }
@@ -37,46 +34,34 @@
     uint32_t onGetFillValue(SkColorType) const override;
 
     // Helper to set up swizzler and color table. Also calls png_read_update_info.
-    bool initializeSwizzler(const SkImageInfo& requestedInfo, const Options&,
-                            SkPMColor*, int* ctableCount);
+    Result initializeSwizzler(const SkImageInfo& requestedInfo, const Options&,
+                              SkPMColor*, int* ctableCount);
     SkSampler* getSampler(bool createIfNecessary) override {
         SkASSERT(fSwizzler);
         return fSwizzler;
     }
 
+    SkPngCodec(int width, int height, const SkEncodedInfo&, SkStream*, SkPngChunkReader*,
+            png_structp, png_infop, int, int, sk_sp<SkColorSpace>);
+
     png_structp png_ptr() { return fPng_ptr; }
-    png_infop info_ptr() { return fInfo_ptr; }
     SkSwizzler* swizzler() { return fSwizzler; }
-
-    /**
-     *  Pass available input to libpng to process it.
-     *
-     *  libpng will call any relevant callbacks installed. This will continue decoding
-     *  until it reaches the end of the file, or until a callback tells libpng to stop.
-     */
-    void processData();
-
-    Result onStartIncrementalDecode(const SkImageInfo& dstInfo, void* pixels, size_t rowBytes,
-            const SkCodec::Options&,
-            SkPMColor* ctable, int* ctableCount) override;
-    Result onIncrementalDecode(int*) override;
+    int numberPasses() const { return fNumberPasses; }
 
 private:
     SkAutoTUnref<SkPngChunkReader>  fPngChunkReader;
     png_structp                     fPng_ptr;
     png_infop                       fInfo_ptr;
 
+    // These are stored here so they can be used both by normal decoding and scanline decoding.
     SkAutoTUnref<SkColorTable>      fColorTable;    // May be unpremul.
     SkAutoTDelete<SkSwizzler>       fSwizzler;
 
-    const int                       fBitDepth;
+    const int                       fNumberPasses;
+    int                             fBitDepth;
 
     bool createColorTable(SkColorType dstColorType, bool premultiply, int* ctableCount);
     void destroyReadStruct();
 
-    virtual Result decodeAllRows(void* dst, size_t rowBytes, int* rowsDecoded) = 0;
-    virtual void setRange(int firstRow, int lastRow, void* dst, size_t rowBytes) = 0;
-    virtual Result decode(int* rowsDecoded) = 0;
-
     typedef SkCodec INHERITED;
 };
diff --git a/src/codec/SkSampledCodec.cpp b/src/codec/SkSampledCodec.cpp
index 8c39f27..49c939c 100644
--- a/src/codec/SkSampledCodec.cpp
+++ b/src/codec/SkSampledCodec.cpp
@@ -101,65 +101,37 @@
     int scaledSubsetWidth = info.width();
     int scaledSubsetHeight = info.height();
 
-    const SkImageInfo scaledInfo = info.makeWH(scaledSize.width(), scaledSize.height());
-
-    {
-        // Although startScanlineDecode expects the bottom and top to match the
-        // SkImageInfo, startIncrementalDecode uses them to determine when to start
-        // and end calling the callback.
-        SkIRect incrementalSubset = SkIRect::MakeXYWH(scaledSubsetX, scaledSubsetY,
-                                                      scaledSubsetWidth, scaledSubsetHeight);
-        codecOptions.fSubset = &incrementalSubset;
-        const SkCodec::Result startResult = this->codec()->startIncrementalDecode(
-                scaledInfo, pixels, rowBytes, &codecOptions,
-                options.fColorPtr, options.fColorCount);
-        if (SkCodec::kSuccess == startResult) {
-            int rowsDecoded;
-            const SkCodec::Result incResult = this->codec()->incrementalDecode(&rowsDecoded);
-            if (incResult == SkCodec::kSuccess) {
-                return SkCodec::kSuccess;
-            }
-            SkASSERT(SkCodec::kIncompleteInput == incResult);
-
-            // FIXME: Can zero initialized be read from SkCodec::fOptions?
-            this->codec()->fillIncompleteImage(scaledInfo, pixels, rowBytes,
-                    options.fZeroInitialized, scaledSubsetHeight, rowsDecoded);
-            return SkCodec::kIncompleteInput;
-        } else if (startResult != SkCodec::kUnimplemented) {
-            return startResult;
-        }
-        // Otherwise fall down to use the old scanline decoder.
-        // codecOptions.fSubset will be reset below, so it will not continue to
-        // point to the object that is no longer on the stack.
-    }
-
     // Start the scanline decode.
     SkIRect scanlineSubset = SkIRect::MakeXYWH(scaledSubsetX, 0, scaledSubsetWidth,
             scaledSize.height());
     codecOptions.fSubset = &scanlineSubset;
-
-    SkCodec::Result result = this->codec()->startScanlineDecode(scaledInfo,
-            &codecOptions, options.fColorPtr, options.fColorCount);
+    SkCodec::Result result = this->codec()->startScanlineDecode(info.makeWH(scaledSize.width(),
+            scaledSize.height()), &codecOptions, options.fColorPtr, options.fColorCount);
     if (SkCodec::kSuccess != result) {
         return result;
     }
 
     // At this point, we are only concerned with subsetting.  Either no scale was
     // requested, or the this->codec() is handling the scale.
-    // Note that subsetting is only supported for kTopDown, so this code will not be
-    // reached for other orders.
-    SkASSERT(this->codec()->getScanlineOrder() == SkCodec::kTopDown_SkScanlineOrder);
-    if (!this->codec()->skipScanlines(scaledSubsetY)) {
-        this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
-                scaledSubsetHeight, 0);
-        return SkCodec::kIncompleteInput;
-    }
+    switch (this->codec()->getScanlineOrder()) {
+        case SkCodec::kTopDown_SkScanlineOrder:
+        case SkCodec::kNone_SkScanlineOrder: {
+            if (!this->codec()->skipScanlines(scaledSubsetY)) {
+                this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
+                        scaledSubsetHeight, 0);
+                return SkCodec::kIncompleteInput;
+            }
 
-    int decodedLines = this->codec()->getScanlines(pixels, scaledSubsetHeight, rowBytes);
-    if (decodedLines != scaledSubsetHeight) {
-        return SkCodec::kIncompleteInput;
+            int decodedLines = this->codec()->getScanlines(pixels, scaledSubsetHeight, rowBytes);
+            if (decodedLines != scaledSubsetHeight) {
+                return SkCodec::kIncompleteInput;
+            }
+            return SkCodec::kSuccess;
+        }
+        default:
+            SkASSERT(false);
+            return SkCodec::kUnimplemented;
     }
-    return SkCodec::kSuccess;
 }
 
 
@@ -202,70 +174,10 @@
         sampledOptions.fSubset = &subset;
     }
 
-    // Since we guarantee that output dimensions are always at least one (even if the sampleSize
-    // is greater than a given dimension), the input sampleSize is not always the sampleSize that
-    // we use in practice.
-    const int sampleX = subsetWidth / info.width();
-    const int sampleY = subsetHeight / info.height();
-
-    const int samplingOffsetY = get_start_coord(sampleY);
-    const int startY = samplingOffsetY + subsetY;
-    int dstHeight = info.height();
-
-    const SkImageInfo nativeInfo = info.makeWH(nativeSize.width(), nativeSize.height());
-
-    {
-        // Although startScanlineDecode expects the bottom and top to match the
-        // SkImageInfo, startIncrementalDecode uses them to determine when to start
-        // and end calling the callback.
-        SkIRect incrementalSubset;
-        incrementalSubset.fTop = startY;
-        incrementalSubset.fBottom = startY + (dstHeight - 1) * sampleY + 1;
-        if (sampledOptions.fSubset) {
-            incrementalSubset.fLeft = sampledOptions.fSubset->fLeft;
-            incrementalSubset.fRight = sampledOptions.fSubset->fRight;
-        } else {
-            incrementalSubset.fLeft = 0;
-            incrementalSubset.fRight = nativeSize.width();
-        }
-        SkCodec::Options incrementalOptions = sampledOptions;
-        incrementalOptions.fSubset = &incrementalSubset;
-        const SkCodec::Result startResult = this->codec()->startIncrementalDecode(nativeInfo,
-                pixels, rowBytes, &incrementalOptions, options.fColorPtr, options.fColorCount);
-        if (SkCodec::kSuccess == startResult) {
-            SkSampler* sampler = this->codec()->getSampler(true);
-            if (!sampler) {
-                return SkCodec::kUnimplemented;
-            }
-
-            if (sampler->setSampleX(sampleX) != info.width()) {
-                return SkCodec::kInvalidScale;
-            }
-            if (get_scaled_dimension(subsetHeight, sampleY) != info.height()) {
-                return SkCodec::kInvalidScale;
-            }
-
-            sampler->setSampleY(sampleY);
-
-            int rowsDecoded;
-            const SkCodec::Result incResult = this->codec()->incrementalDecode(&rowsDecoded);
-            if (incResult == SkCodec::kSuccess) {
-                return SkCodec::kSuccess;
-            }
-            SkASSERT(incResult == SkCodec::kIncompleteInput);
-            const int lastRowInOutput = (rowsDecoded - startY) / sampleY;
-            // FIXME: Should this be info or nativeInfo? Does it make a difference?
-            this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
-                                               info.height(), lastRowInOutput);
-            return SkCodec::kIncompleteInput;
-        } else if (startResult != SkCodec::kUnimplemented) {
-            return startResult;
-        } // kUnimplemented means use the old method.
-    }
-
     // Start the scanline decode.
-    SkCodec::Result result = this->codec()->startScanlineDecode(nativeInfo,
-            &sampledOptions, options.fColorPtr, options.fColorCount);
+    SkCodec::Result result = this->codec()->startScanlineDecode(
+            info.makeWH(nativeSize.width(), nativeSize.height()), &sampledOptions,
+            options.fColorPtr, options.fColorCount);
     if (SkCodec::kSuccess != result) {
         return result;
     }
@@ -275,6 +187,11 @@
         return SkCodec::kUnimplemented;
     }
 
+    // Since we guarantee that output dimensions are always at least one (even if the sampleSize
+    // is greater than a given dimension), the input sampleSize is not always the sampleSize that
+    // we use in practice.
+    const int sampleX = subsetWidth / info.width();
+    const int sampleY = subsetHeight / info.height();
     if (sampler->setSampleX(sampleX) != info.width()) {
         return SkCodec::kInvalidScale;
     }
@@ -282,6 +199,9 @@
         return SkCodec::kInvalidScale;
     }
 
+    const int samplingOffsetY = get_start_coord(sampleY);
+    const int startY = samplingOffsetY + subsetY;
+    int dstHeight = info.height();
     switch(this->codec()->getScanlineOrder()) {
         case SkCodec::kTopDown_SkScanlineOrder: {
             if (!this->codec()->skipScanlines(startY)) {
@@ -346,6 +266,30 @@
             }
             return SkCodec::kIncompleteInput;
         }
+        case SkCodec::kNone_SkScanlineOrder: {
+            const int linesNeeded = subsetHeight - samplingOffsetY;
+            SkAutoTMalloc<uint8_t> storage(linesNeeded * rowBytes);
+            uint8_t* storagePtr = storage.get();
+
+            if (!this->codec()->skipScanlines(startY)) {
+                this->codec()->fillIncompleteImage(info, pixels, rowBytes, options.fZeroInitialized,
+                        dstHeight, 0);
+                return SkCodec::kIncompleteInput;
+            }
+            int scanlines = this->codec()->getScanlines(storagePtr, linesNeeded, rowBytes);
+
+            for (int y = 0; y < dstHeight; y++) {
+                memcpy(pixels, storagePtr, info.minRowBytes());
+                storagePtr += sampleY * rowBytes;
+                pixels = SkTAddOffset<void>(pixels, rowBytes);
+            }
+
+            if (scanlines < dstHeight) {
+                // this->codec() has already handled filling uninitialized memory.
+                return SkCodec::kIncompleteInput;
+            }
+            return SkCodec::kSuccess;
+        }
         default:
             SkASSERT(false);
             return SkCodec::kUnimplemented;
diff --git a/src/codec/SkSampler.h b/src/codec/SkSampler.h
index af6f485..73e11c9 100644
--- a/src/codec/SkSampler.h
+++ b/src/codec/SkSampler.h
@@ -21,30 +21,6 @@
     }
 
     /**
-     *  Update the sampler to sample every sampleY'th row.
-     */
-    void setSampleY(int sampleY) {
-        fSampleY = sampleY;
-    }
-
-    /**
-     *  Retrieve the value set for sampleY.
-     */
-    int sampleY() const {
-        return fSampleY;
-    }
-
-    /**
-     *  Based on fSampleY, return whether this row belongs in the output.
-     *
-     *  @param row Row of the image, starting with the first row used in the
-     *      output.
-     */
-    bool rowNeeded(int row) const {
-        return row % fSampleY == 0;
-    }
-
-    /**
      * Fill the remainder of the destination with a single color
      *
      * @param info
@@ -78,13 +54,8 @@
     virtual void fill(const SkImageInfo& info, void* dst, size_t rowBytes,
             uint32_t colorOrIndex, SkCodec::ZeroInitialized zeroInit) {}
 
-    SkSampler()
-        : fSampleY(1)
-    {}
-
     virtual ~SkSampler() {}
 private:
-    int fSampleY;
 
     virtual int onSetSampleX(int) = 0;
 };
diff --git a/tests/CodecPartial.cpp b/tests/CodecPartial.cpp
deleted file mode 100644
index 8775e87..0000000
--- a/tests/CodecPartial.cpp
+++ /dev/null
@@ -1,155 +0,0 @@
-/*
- * Copyright 2016 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#include "SkBitmap.h"
-#include "SkCodec.h"
-#include "SkData.h"
-#include "SkImageInfo.h"
-#include "SkRWBuffer.h"
-#include "SkString.h"
-
-#include "Resources.h"
-#include "Test.h"
-
-static sk_sp<SkData> make_from_resource(const char* name) {
-    SkString fullPath = GetResourcePath(name);
-    return SkData::MakeFromFileName(fullPath.c_str());
-}
-
-static SkImageInfo standardize_info(SkCodec* codec) {
-    SkImageInfo defaultInfo = codec->getInfo();
-    // Note: This drops the SkColorSpace, allowing the equality check between two
-    // different codecs created from the same file to have the same SkImageInfo.
-    return SkImageInfo::MakeN32Premul(defaultInfo.width(), defaultInfo.height());
-}
-
-static bool create_truth(sk_sp<SkData> data, SkBitmap* dst) {
-    SkAutoTDelete<SkCodec> codec(SkCodec::NewFromData(data.get()));
-    if (!codec) {
-        return false;
-    }
-
-    const SkImageInfo info = standardize_info(codec);
-    dst->allocPixels(info);
-    return SkCodec::kSuccess == codec->getPixels(info, dst->getPixels(), dst->rowBytes());
-}
-
-/*
- *  Represents a stream without all of its data.
- */
-class HaltingStream : public SkStream {
-public:
-    HaltingStream(sk_sp<SkData> data)
-        : fTotalSize(data->size())
-        , fLimit(fTotalSize / 2)
-        , fStream(std::move(data))
-    {}
-
-    void addNewData() {
-        // Arbitrary size, but deliberately different from
-        // the buffer size used by SkPngCodec.
-        fLimit = SkTMin(fTotalSize, fLimit + 1000);
-    }
-
-    size_t read(void* buffer, size_t size) override {
-        if (fStream.getPosition() + size > fLimit) {
-            size = fLimit - fStream.getPosition();
-        }
-
-        return fStream.read(buffer, size);
-    }
-
-    bool isAtEnd() const override {
-        return fStream.isAtEnd();
-    }
-
-    bool hasPosition() const override { return true; }
-    size_t getPosition() const override { return fStream.getPosition(); }
-    bool rewind() override { return fStream.rewind(); }
-    bool move(long offset) override { return fStream.move(offset); }
-
-private:
-    const size_t    fTotalSize;
-    size_t          fLimit;
-    SkMemoryStream  fStream;
-};
-
-static void test_partial(skiatest::Reporter* r, const char* name) {
-    sk_sp<SkData> file = make_from_resource(name);
-    if (!file) {
-        SkDebugf("missing resource %s\n", name);
-        return;
-    }
-
-    SkBitmap truth;
-    if (!create_truth(file, &truth)) {
-        ERRORF(r, "Failed to decode %s\n", name);
-        return;
-    }
-
-    const size_t fileSize = file->size();
-
-    // Now decode part of the file
-    HaltingStream* stream = new HaltingStream(file);
-
-    // Note that we cheat and hold on to a pointer to stream, though it is owned by
-    // partialCodec.
-    SkAutoTDelete<SkCodec> partialCodec(SkCodec::NewFromStream(stream));
-    if (!partialCodec) {
-        // Technically, this could be a small file where half the file is not
-        // enough.
-        ERRORF(r, "Failed to create codec for %s", name);
-        return;
-    }
-
-    const SkImageInfo info = standardize_info(partialCodec);
-    SkASSERT(info == truth.info());
-    SkBitmap incremental;
-    incremental.allocPixels(info);
-
-    const SkCodec::Result startResult = partialCodec->startIncrementalDecode(info,
-            incremental.getPixels(), incremental.rowBytes());
-    if (startResult != SkCodec::kSuccess) {
-        ERRORF(r, "Failed to start incremental decode\n");
-        return;
-    }
-
-    while (true) {
-        const SkCodec::Result result = partialCodec->incrementalDecode();
-
-        if (stream->getPosition() == fileSize) {
-            REPORTER_ASSERT(r, result == SkCodec::kSuccess);
-            break;
-        }
-
-        SkASSERT(stream->getPosition() < fileSize);
-
-        REPORTER_ASSERT(r, result == SkCodec::kIncompleteInput);
-
-        // Append an arbitrary amount of data.
-        stream->addNewData();
-    }
-
-    // compare to original
-    for (int i = 0; i < info.height(); i++) {
-        REPORTER_ASSERT(r, !memcmp(truth.getAddr(0, 0), incremental.getAddr(0, 0),
-                                   info.minRowBytes()));
-    }
-}
-
-DEF_TEST(Codec_partial, r) {
-    test_partial(r, "plane.png");
-    test_partial(r, "plane_interlaced.png");
-    test_partial(r, "yellow_rose.png");
-    test_partial(r, "index8.png");
-    test_partial(r, "color_wheel.png");
-    test_partial(r, "mandrill_256.png");
-    test_partial(r, "mandrill_32.png");
-    test_partial(r, "arrow.png");
-    test_partial(r, "randPixels.png");
-    test_partial(r, "baby_tux.png");
-}
diff --git a/tests/CodecTest.cpp b/tests/CodecTest.cpp
index 52ddbff..12d6ac8 100644
--- a/tests/CodecTest.cpp
+++ b/tests/CodecTest.cpp
@@ -83,62 +83,6 @@
     return rect;
 }
 
-static void test_incremental_decode(skiatest::Reporter* r, SkCodec* codec, const SkImageInfo& info,
-        const SkMD5::Digest& goodDigest) {
-    SkBitmap bm;
-    bm.allocPixels(info);
-    SkAutoLockPixels autoLockPixels(bm);
-
-    REPORTER_ASSERT(r, SkCodec::kSuccess == codec->startIncrementalDecode(info, bm.getPixels(),
-                                                                          bm.rowBytes()));
-
-    REPORTER_ASSERT(r, SkCodec::kSuccess == codec->incrementalDecode());
-
-    compare_to_good_digest(r, goodDigest, bm);
-}
-
-// Test in stripes, similar to DM's kStripe_Mode
-static void test_in_stripes(skiatest::Reporter* r, SkCodec* codec, const SkImageInfo& info,
-                            const SkMD5::Digest& goodDigest) {
-    SkBitmap bm;
-    bm.allocPixels(info);
-    bm.eraseColor(SK_ColorYELLOW);
-
-    const int height = info.height();
-    // Note that if numStripes does not evenly divide height there will be an extra
-    // stripe.
-    const int numStripes = 4;
-
-    if (numStripes > height) {
-        // Image is too small.
-        return;
-    }
-
-    const int stripeHeight = height / numStripes;
-
-    // Iterate through the image twice. Once to decode odd stripes, and once for even.
-    for (int oddEven = 1; oddEven >= 0; oddEven--) {
-        for (int y = oddEven * stripeHeight; y < height; y += 2 * stripeHeight) {
-            SkIRect subset = SkIRect::MakeLTRB(0, y, info.width(),
-                                               SkTMin(y + stripeHeight, height));
-            SkCodec::Options options;
-            options.fSubset = &subset;
-            if (SkCodec::kSuccess != codec->startIncrementalDecode(info, bm.getAddr(0, y),
-                        bm.rowBytes(), &options)) {
-                ERRORF(r, "failed to start incremental decode!\ttop: %i\tbottom%i\n",
-                       subset.top(), subset.bottom());
-                return;
-            }
-            if (SkCodec::kSuccess != codec->incrementalDecode()) {
-                ERRORF(r, "failed incremental decode starting from line %i\n", y);
-                return;
-            }
-        }
-    }
-
-    compare_to_good_digest(r, goodDigest, bm);
-}
-
 template<typename Codec>
 static void test_codec(skiatest::Reporter* r, Codec* codec, SkBitmap& bm, const SkImageInfo& info,
         const SkISize& size, SkCodec::Result expectedResult, SkMD5::Digest* digest,
@@ -247,14 +191,12 @@
     return false;
 }
 
-// FIXME: Break up this giant function
 static void check(skiatest::Reporter* r,
                   const char path[],
                   SkISize size,
                   bool supportsScanlineDecoding,
                   bool supportsSubsetDecoding,
-                  bool supportsIncomplete,
-                  bool supportsNewScanlineDecoding = false) {
+                  bool supportsIncomplete = true) {
 
     SkAutoTDelete<SkStream> stream(resource(path));
     if (!stream) {
@@ -284,15 +226,12 @@
     test_codec(r, codec.get(), bm, info, size, expectedResult, &codecDigest, nullptr);
 
     // Scanline decoding follows.
-
-    if (supportsNewScanlineDecoding && !isIncomplete) {
-        test_incremental_decode(r, codec, info, codecDigest);
-        test_in_stripes(r, codec, info, codecDigest);
-    }
-
     // Need to call startScanlineDecode() first.
-    REPORTER_ASSERT(r, codec->getScanlines(bm.getAddr(0, 0), 1, 0) == 0);
-    REPORTER_ASSERT(r, !codec->skipScanlines(1));
+    REPORTER_ASSERT(r, codec->getScanlines(bm.getAddr(0, 0), 1, 0)
+            == 0);
+    REPORTER_ASSERT(r, codec->skipScanlines(1)
+            == 0);
+
     const SkCodec::Result startResult = codec->startScanlineDecode(info);
     if (supportsScanlineDecoding) {
         bm.eraseColor(SK_ColorYELLOW);
@@ -387,7 +326,7 @@
     }
 
     // SkAndroidCodec tests
-    if (supportsScanlineDecoding || supportsSubsetDecoding || supportsNewScanlineDecoding) {
+    if (supportsScanlineDecoding || supportsSubsetDecoding) {
 
         SkAutoTDelete<SkStream> stream(resource(path));
         if (!stream) {
@@ -425,23 +364,14 @@
         REPORTER_ASSERT(r, gen->getPixels(info, bm.getPixels(), bm.rowBytes()));
         compare_to_good_digest(r, codecDigest, bm);
 
-#if PNG_LIBPNG_VER_MAJOR == 1 && PNG_LIBPNG_VER_MINOR < 5
-        // FIXME: With older versions of libpng, SkPngCodec requires being able to call
-        // SkStream::move(), which is not supported by SkFrontBufferedStream. (Android
-        // has a more recent version of libpng which uses png_process_data_pause to
-        // avoid calling move().)
-        if (!SkStrEndsWith(path, ".png"))
-#endif
-        {
-            // Test using SkFrontBufferedStream, as Android does
-            SkStream* bufferedStream = SkFrontBufferedStream::Create(new SkMemoryStream(fullData),
-                    SkCodec::MinBufferedBytesNeeded());
-            REPORTER_ASSERT(r, bufferedStream);
-            codec.reset(SkCodec::NewFromStream(bufferedStream));
-            REPORTER_ASSERT(r, codec);
-            if (codec) {
-                test_info(r, codec.get(), info, SkCodec::kSuccess, &codecDigest);
-            }
+        // Test using SkFrontBufferedStream, as Android does
+        SkStream* bufferedStream = SkFrontBufferedStream::Create(new SkMemoryStream(fullData),
+                SkCodec::MinBufferedBytesNeeded());
+        REPORTER_ASSERT(r, bufferedStream);
+        codec.reset(SkCodec::NewFromStream(bufferedStream));
+        REPORTER_ASSERT(r, codec);
+        if (codec) {
+            test_info(r, codec.get(), info, SkCodec::kSuccess, &codecDigest);
         }
     }
 
@@ -453,16 +383,16 @@
 
 DEF_TEST(Codec, r) {
     // WBMP
-    check(r, "mandrill.wbmp", SkISize::Make(512, 512), true, false, true);
+    check(r, "mandrill.wbmp", SkISize::Make(512, 512), true, false);
 
     // WEBP
-    check(r, "baby_tux.webp", SkISize::Make(386, 395), false, true, true);
-    check(r, "color_wheel.webp", SkISize::Make(128, 128), false, true, true);
-    check(r, "yellow_rose.webp", SkISize::Make(400, 301), false, true, true);
+    check(r, "baby_tux.webp", SkISize::Make(386, 395), false, true);
+    check(r, "color_wheel.webp", SkISize::Make(128, 128), false, true);
+    check(r, "yellow_rose.webp", SkISize::Make(400, 301), false, true);
 
     // BMP
-    check(r, "randPixels.bmp", SkISize::Make(8, 8), true, false, true);
-    check(r, "rle.bmp", SkISize::Make(320, 240), true, false, true);
+    check(r, "randPixels.bmp", SkISize::Make(8, 8), true, false);
+    check(r, "rle.bmp", SkISize::Make(320, 240), true, false);
 
     // ICO
     // FIXME: We are not ready to test incomplete ICOs
@@ -470,7 +400,7 @@
     // Decodes an embedded BMP image
     check(r, "color_wheel.ico", SkISize::Make(128, 128), true, false, false);
     // Decodes an embedded PNG image
-    check(r, "google_chrome.ico", SkISize::Make(256, 256), false, false, false, true);
+    check(r, "google_chrome.ico", SkISize::Make(256, 256), true, false, false);
 
     // GIF
     // FIXME: We are not ready to test incomplete GIFs
@@ -480,30 +410,30 @@
     check(r, "randPixels.gif", SkISize::Make(8, 8), true, false, false);
 
     // JPG
-    check(r, "CMYK.jpg", SkISize::Make(642, 516), true, false, true);
-    check(r, "color_wheel.jpg", SkISize::Make(128, 128), true, false, true);
+    check(r, "CMYK.jpg", SkISize::Make(642, 516), true, false);
+    check(r, "color_wheel.jpg", SkISize::Make(128, 128), true, false);
     // grayscale.jpg is too small to test incomplete
     check(r, "grayscale.jpg", SkISize::Make(128, 128), true, false, false);
-    check(r, "mandrill_512_q075.jpg", SkISize::Make(512, 512), true, false, true);
+    check(r, "mandrill_512_q075.jpg", SkISize::Make(512, 512), true, false);
     // randPixels.jpg is too small to test incomplete
     check(r, "randPixels.jpg", SkISize::Make(8, 8), true, false, false);
 
     // PNG
-    check(r, "arrow.png", SkISize::Make(187, 312), false, false, true, true);
-    check(r, "baby_tux.png", SkISize::Make(240, 246), false, false, true, true);
-    check(r, "color_wheel.png", SkISize::Make(128, 128), false, false, true, true);
-    // half-transparent-white-pixel.png is too small to test incomplete
-    check(r, "half-transparent-white-pixel.png", SkISize::Make(1, 1), false, false, false, true);
-    check(r, "mandrill_128.png", SkISize::Make(128, 128), false, false, true, true);
-    check(r, "mandrill_16.png", SkISize::Make(16, 16), false, false, true, true);
-    check(r, "mandrill_256.png", SkISize::Make(256, 256), false, false, true, true);
-    check(r, "mandrill_32.png", SkISize::Make(32, 32), false, false, true, true);
-    check(r, "mandrill_512.png", SkISize::Make(512, 512), false, false, true, true);
-    check(r, "mandrill_64.png", SkISize::Make(64, 64), false, false, true, true);
-    check(r, "plane.png", SkISize::Make(250, 126), false, false, true, true);
-    check(r, "plane_interlaced.png", SkISize::Make(250, 126), false, false, true, true);
-    check(r, "randPixels.png", SkISize::Make(8, 8), false, false, true, true);
-    check(r, "yellow_rose.png", SkISize::Make(400, 301), false, false, true, true);
+    check(r, "arrow.png", SkISize::Make(187, 312), true, false, false);
+    check(r, "baby_tux.png", SkISize::Make(240, 246), true, false, false);
+    check(r, "color_wheel.png", SkISize::Make(128, 128), true, false, false);
+    check(r, "half-transparent-white-pixel.png", SkISize::Make(1, 1), true, false, false);
+    check(r, "mandrill_128.png", SkISize::Make(128, 128), true, false, false);
+    check(r, "mandrill_16.png", SkISize::Make(16, 16), true, false, false);
+    check(r, "mandrill_256.png", SkISize::Make(256, 256), true, false, false);
+    check(r, "mandrill_32.png", SkISize::Make(32, 32), true, false, false);
+    check(r, "mandrill_512.png", SkISize::Make(512, 512), true, false, false);
+    check(r, "mandrill_64.png", SkISize::Make(64, 64), true, false, false);
+    check(r, "plane.png", SkISize::Make(250, 126), true, false, false);
+    // FIXME: We are not ready to test incomplete interlaced pngs
+    check(r, "plane_interlaced.png", SkISize::Make(250, 126), true, false, false);
+    check(r, "randPixels.png", SkISize::Make(8, 8), true, false, false);
+    check(r, "yellow_rose.png", SkISize::Make(400, 301), true, false, false);
 
     // RAW
 // Disable RAW tests for Win32.
@@ -514,6 +444,97 @@
 #endif
 }
 
+// Test interlaced PNG in stripes, similar to DM's kStripe_Mode
+DEF_TEST(Codec_stripes, r) {
+    const char * path = "plane_interlaced.png";
+    SkAutoTDelete<SkStream> stream(resource(path));
+    if (!stream) {
+        SkDebugf("Missing resource '%s'\n", path);
+    }
+
+    SkAutoTDelete<SkCodec> codec(SkCodec::NewFromStream(stream.release()));
+    REPORTER_ASSERT(r, codec);
+
+    if (!codec) {
+        return;
+    }
+
+    switch (codec->getScanlineOrder()) {
+        case SkCodec::kBottomUp_SkScanlineOrder:
+        case SkCodec::kOutOfOrder_SkScanlineOrder:
+            ERRORF(r, "This scanline order will not match the original.");
+            return;
+        default:
+            break;
+    }
+
+    // Baseline for what the image should look like, using N32.
+    const SkImageInfo info = codec->getInfo().makeColorType(kN32_SkColorType);
+
+    SkBitmap bm;
+    bm.allocPixels(info);
+    SkAutoLockPixels autoLockPixels(bm);
+    SkCodec::Result result = codec->getPixels(info, bm.getPixels(), bm.rowBytes());
+    REPORTER_ASSERT(r, result == SkCodec::kSuccess);
+
+    SkMD5::Digest digest;
+    md5(bm, &digest);
+
+    // Now decode in stripes
+    const int height = info.height();
+    const int numStripes = 4;
+    int stripeHeight;
+    int remainingLines;
+    SkTDivMod(height, numStripes, &stripeHeight, &remainingLines);
+
+    bm.eraseColor(SK_ColorYELLOW);
+
+    result = codec->startScanlineDecode(info);
+    REPORTER_ASSERT(r, result == SkCodec::kSuccess);
+
+    // Odd stripes
+    for (int i = 1; i < numStripes; i += 2) {
+        // Skip the even stripes
+        bool skipResult = codec->skipScanlines(stripeHeight);
+        REPORTER_ASSERT(r, skipResult);
+
+        int linesDecoded = codec->getScanlines(bm.getAddr(0, i * stripeHeight), stripeHeight,
+                                     bm.rowBytes());
+        REPORTER_ASSERT(r, linesDecoded == stripeHeight);
+    }
+
+    // Even stripes
+    result = codec->startScanlineDecode(info);
+    REPORTER_ASSERT(r, result == SkCodec::kSuccess);
+
+    for (int i = 0; i < numStripes; i += 2) {
+        int linesDecoded = codec->getScanlines(bm.getAddr(0, i * stripeHeight), stripeHeight,
+                                     bm.rowBytes());
+        REPORTER_ASSERT(r, linesDecoded == stripeHeight);
+
+        // Skip the odd stripes
+        if (i + 1 < numStripes) {
+            bool skipResult = codec->skipScanlines(stripeHeight);
+            REPORTER_ASSERT(r, skipResult);
+        }
+    }
+
+    // Remainder at the end
+    if (remainingLines > 0) {
+        result = codec->startScanlineDecode(info);
+        REPORTER_ASSERT(r, result == SkCodec::kSuccess);
+
+        bool skipResult = codec->skipScanlines(height - remainingLines);
+        REPORTER_ASSERT(r, skipResult);
+
+        int linesDecoded = codec->getScanlines(bm.getAddr(0, height - remainingLines),
+                                     remainingLines, bm.rowBytes());
+        REPORTER_ASSERT(r, linesDecoded == remainingLines);
+    }
+
+    compare_to_good_digest(r, digest, bm);
+}
+
 static void test_invalid_stream(skiatest::Reporter* r, const void* stream, size_t len) {
     // Neither of these calls should return a codec. Bots should catch us if we leaked anything.
     SkCodec* codec = SkCodec::NewFromStream(new SkMemoryStream(stream, len, false));
@@ -656,41 +677,26 @@
         return;
     }
     SkAutoTDelete<SkCodec> decoder(SkCodec::NewFromStream(stream.release()));
-    if (!decoder) {
-        SkDebugf("Missing codec for %s\n", path);
-        return;
-    }
-
-    const SkImageInfo info = decoder->getInfo().makeColorType(kIndex_8_SkColorType);
 
     // This should return kSuccess because kIndex8 is supported.
     SkPMColor colorStorage[256];
     int colorCount;
-    SkCodec::Result result = decoder->startScanlineDecode(info, nullptr, colorStorage,
-                                                          &colorCount);
-    if (SkCodec::kSuccess == result) {
-        // This should return kInvalidParameters because, in kIndex_8 mode, we must pass in a valid
-        // colorPtr and a valid colorCountPtr.
-        result = decoder->startScanlineDecode(info, nullptr, nullptr, nullptr);
-        REPORTER_ASSERT(r, SkCodec::kInvalidParameters == result);
-        result = decoder->startScanlineDecode(info);
-        REPORTER_ASSERT(r, SkCodec::kInvalidParameters == result);
-    } else if (SkCodec::kUnimplemented == result) {
-        // New method should be supported:
-        SkBitmap bm;
-        sk_sp<SkColorTable> colorTable(new SkColorTable(colorStorage, 256));
-        bm.allocPixels(info, nullptr, colorTable.get());
-        result = decoder->startIncrementalDecode(info, bm.getPixels(), bm.rowBytes(), nullptr,
-                                                 colorStorage, &colorCount);
-        REPORTER_ASSERT(r, SkCodec::kSuccess == result);
-        result = decoder->startIncrementalDecode(info, bm.getPixels(), bm.rowBytes());
-        REPORTER_ASSERT(r, SkCodec::kInvalidParameters == result);
-    } else {
-        // The test is uninteresting if kIndex8 is not supported
-        ERRORF(r, "Should not call test_invalid_parameters for non-Index8 file: %s\n", path);
+    SkCodec::Result result = decoder->startScanlineDecode(
+        decoder->getInfo().makeColorType(kIndex_8_SkColorType), nullptr, colorStorage, &colorCount);
+    REPORTER_ASSERT(r, SkCodec::kSuccess == result);
+    // The rest of the test is uninteresting if kIndex8 is not supported
+    if (SkCodec::kSuccess != result) {
         return;
     }
 
+    // This should return kInvalidParameters because, in kIndex_8 mode, we must pass in a valid
+    // colorPtr and a valid colorCountPtr.
+    result = decoder->startScanlineDecode(
+        decoder->getInfo().makeColorType(kIndex_8_SkColorType), nullptr, nullptr, nullptr);
+    REPORTER_ASSERT(r, SkCodec::kInvalidParameters == result);
+    result = decoder->startScanlineDecode(
+        decoder->getInfo().makeColorType(kIndex_8_SkColorType));
+    REPORTER_ASSERT(r, SkCodec::kInvalidParameters == result);
 }
 
 DEF_TEST(Codec_Params, r) {
@@ -1006,91 +1012,3 @@
 
     REPORTER_ASSERT(r, !codec);
 }
-
-// Only rewinds up to a limit.
-class LimitedRewindingStream : public SkStream {
-public:
-    static SkStream* Make(const char path[], size_t limit) {
-        SkStream* stream = resource(path);
-        if (!stream) {
-            return nullptr;
-        }
-        return new LimitedRewindingStream(stream, limit);
-    }
-
-    size_t read(void* buffer, size_t size) override {
-        const size_t bytes = fStream->read(buffer, size);
-        fPosition += bytes;
-        return bytes;
-    }
-
-    bool isAtEnd() const override {
-        return fStream->isAtEnd();
-    }
-
-    bool rewind() override {
-        if (fPosition <= fLimit && fStream->rewind()) {
-            fPosition = 0;
-            return true;
-        }
-
-        return false;
-    }
-
-private:
-    SkAutoTDelete<SkStream> fStream;
-    const size_t            fLimit;
-    size_t                  fPosition;
-
-    LimitedRewindingStream(SkStream* stream, size_t limit)
-        : fStream(stream)
-        , fLimit(limit)
-        , fPosition(0)
-    {
-        SkASSERT(fStream);
-    }
-};
-
-DEF_TEST(Codec_fallBack, r) {
-    // SkAndroidCodec needs to be able to fall back to scanline decoding
-    // if incremental decoding does not work. Make sure this does not
-    // require a rewind.
-
-    // Formats that currently do not support incremental decoding
-    auto files = {
-            "box.gif",
-            "CMYK.jpg",
-            "color_wheel.ico",
-            "mandrill.wbmp",
-            "randPixels.bmp",
-            };
-    for (auto file : files) {
-        SkStream* stream = LimitedRewindingStream::Make(file, 14);
-        if (!stream) {
-            SkDebugf("Missing resources (%s). Set --resourcePath.\n", file);
-            return;
-        }
-
-        SkAutoTDelete<SkCodec> codec(SkCodec::NewFromStream(stream));
-        if (!codec) {
-            ERRORF(r, "Failed to create codec for %s,", file);
-            continue;
-        }
-
-        SkImageInfo info = codec->getInfo().makeColorType(kN32_SkColorType);
-        SkBitmap bm;
-        bm.allocPixels(info);
-
-        if (SkCodec::kUnimplemented != codec->startIncrementalDecode(info, bm.getPixels(),
-                bm.rowBytes())) {
-            ERRORF(r, "Is scanline decoding now implemented for %s?", file);
-            continue;
-        }
-
-        // Scanline decoding should not require a rewind.
-        SkCodec::Result result = codec->startScanlineDecode(info);
-        if (SkCodec::kSuccess != result) {
-            ERRORF(r, "Scanline decoding failed for %s with %i", file, result);
-        }
-    }
-}
diff --git a/tests/ColorSpaceTest.cpp b/tests/ColorSpaceTest.cpp
index 8cb1b9a..b26cec2 100644
--- a/tests/ColorSpaceTest.cpp
+++ b/tests/ColorSpaceTest.cpp
@@ -67,10 +67,7 @@
     }
 
     SkAutoTDelete<SkCodec> codec(SkCodec::NewFromStream(stream.release()));
-    if (!codec) {
-        ERRORF(r, "Failed to create codec from a PNG. Is PNG support missing (or too old)?");
-        return;
-    }
+    REPORTER_ASSERT(r, nullptr != codec);
 
 #if (PNG_LIBPNG_VER_MAJOR > 1) || (PNG_LIBPNG_VER_MAJOR == 1 && PNG_LIBPNG_VER_MINOR >= 6)
     SkColorSpace* colorSpace = codec->getColorSpace();
diff --git a/tests/ImageTest.cpp b/tests/ImageTest.cpp
index b2bf495..0922364 100644
--- a/tests/ImageTest.cpp
+++ b/tests/ImageTest.cpp
@@ -161,10 +161,6 @@
     REPORTER_ASSERT(reporter, origEncoded->size() > 0);
 
     sk_sp<SkImage> decoded(SkImage::MakeFromEncoded(origEncoded));
-    if (!decoded) {
-        ERRORF(reporter, "failed to decode image!");
-        return;
-    }
     REPORTER_ASSERT(reporter, decoded);
     assert_equal(reporter, image, nullptr, decoded.get());
 
@@ -522,10 +518,6 @@
 }
 
 static void test_read_pixels(skiatest::Reporter* reporter, SkImage* image) {
-    if (!image) {
-        ERRORF(reporter, "Failed to create image!");
-        return;
-    }
     const SkPMColor expected = SkPreMultiplyColor(SK_ColorWHITE);
     const SkPMColor notExpected = ~expected;
 
@@ -611,10 +603,6 @@
 }
 
 static void test_legacy_bitmap(skiatest::Reporter* reporter, const SkImage* image, SkImage::LegacyBitmapMode mode) {
-    if (!image) {
-        ERRORF(reporter, "Failed to create image.");
-        return;
-    }
     SkBitmap bitmap;
     REPORTER_ASSERT(reporter, image->asLegacyBitmap(&bitmap, mode));
     check_legacy_bitmap(reporter, image, bitmap, mode);
@@ -666,10 +654,6 @@
 #endif
 
 static void test_peek(skiatest::Reporter* reporter, SkImage* image, bool expectPeekSuccess) {
-    if (!image) {
-        ERRORF(reporter, "Failed to create image!");
-        return;
-    }
     SkPixmap pm;
     bool success = image->peekPixels(&pm);
     REPORTER_ASSERT(reporter, expectPeekSuccess == success);
@@ -873,10 +857,6 @@
 
     for (auto testCase : testCases) {
         sk_sp<SkImage> image(testCase.fImageFactory());
-        if (!image) {
-            ERRORF(reporter, "Failed to create image!");
-            continue;
-        }
 
         // This isn't currently used in the implementation, just set any old values.
         SkImage::DeferredTextureImageUsageParams params;