SkCodec no longer inherits from SkImageGenerator.

SkImageGenerator makes some assumptions that are not necessarily valid
for SkCodec. For example, SkCodec does not assume that it can always be
rewound.

We also have an ongoing question of what an SkCodec should report as
its default settings (i.e. the return from getInfo). It makes sense for
an SkCodec to report that its pixels are unpremultiplied, if that is
the case for the underlying data, but if a client of SkImageGenerator
uses the default settings (as many do), they will receive
unpremultiplied pixels which cannot (currently) be drawn with Skia. We
may ultimately decide to revisit SkCodec reporting an SkImageInfo, but
I have left it unchanged for now.

Import features of SkImageGenerator used by SkCodec into SkCodec.

I have left SkImageGenerator unchanged for now, but it no longer needs
Result or Options. This will require changes to Chromium.

Manually handle the lifetime of fScanlineDecoder, so SkScanlineDecoder.h
can include SkCodec.h (where Result is), and SkCodec.h does not need
to include it (to delete fScanlineDecoder).

In many places, make the following simple changes:
- Now include SkScanlineDecoder.h, which is no longer included by
  SkCodec.h
- Use the enums in SkCodec, rather than SkImageGenerator
- Stop including SkImageGenerator.h where no longer needed

Review URL: https://codereview.chromium.org/1220733013
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index f83ba3b..f7daad7 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -143,12 +143,12 @@
         case kNormal_Mode: {
             switch (codec->getPixels(decodeInfo, bitmap.getPixels(), bitmap.rowBytes(), NULL,
                     colorPtr, colorCountPtr)) {
-                case SkImageGenerator::kSuccess:
+                case SkCodec::kSuccess:
                     // We consider incomplete to be valid, since we should still decode what is
                     // available.
-                case SkImageGenerator::kIncompleteInput:
+                case SkCodec::kIncompleteInput:
                     break;
-                case SkImageGenerator::kInvalidConversion:
+                case SkCodec::kInvalidConversion:
                     return Error::Nonfatal("Incompatible colortype conversion");
                 default:
                     // Everything else is considered a failure.
@@ -163,11 +163,11 @@
             if (NULL == scanlineDecoder) {
                 return Error::Nonfatal("Cannot use scanline decoder for all images");
             }
-            const SkImageGenerator::Result result = scanlineDecoder->getScanlines(
+            const SkCodec::Result result = scanlineDecoder->getScanlines(
                     bitmap.getAddr(0, 0), decodeInfo.height(), bitmap.rowBytes());
             switch (result) {
-                case SkImageGenerator::kSuccess:
-                case SkImageGenerator::kIncompleteInput:
+                case SkCodec::kSuccess:
+                case SkCodec::kIncompleteInput:
                     break;
                 default:
                     return SkStringPrintf("%s failed with error message %d",
@@ -231,11 +231,11 @@
                         }
                     }
                     //skip to first line of subset
-                    const SkImageGenerator::Result skipResult =
+                    const SkCodec::Result skipResult =
                             subsetScanlineDecoder->skipScanlines(y);
                     switch (skipResult) {
-                        case SkImageGenerator::kSuccess:
-                        case SkImageGenerator::kIncompleteInput:
+                        case SkCodec::kSuccess:
+                        case SkCodec::kIncompleteInput:
                             break;
                         default:
                             return SkStringPrintf("%s failed after attempting to skip %d scanlines"
@@ -247,11 +247,11 @@
                     bounds.setXYWH(0, 0, currentSubsetWidth, currentSubsetHeight);
                     SkAssertResult(largestSubsetBm.extractSubset(&subsetBm, bounds));
                     SkAutoLockPixels autlockSubsetBm(subsetBm, true);
-                    const SkImageGenerator::Result subsetResult =
+                    const SkCodec::Result subsetResult =
                         subsetScanlineDecoder->getScanlines(buffer, currentSubsetHeight, rowBytes);
                     switch (subsetResult) {
-                        case SkImageGenerator::kSuccess:
-                        case SkImageGenerator::kIncompleteInput:
+                        case SkCodec::kSuccess:
+                        case SkCodec::kIncompleteInput:
                             break;
                         default:
                             return SkStringPrintf("%s failed with error message %d",
@@ -295,10 +295,10 @@
             for (int i = 0; i < numStripes; i += 2) {
                 // Skip a stripe
                 const int linesToSkip = SkTMin(stripeHeight, height - i * stripeHeight);
-                SkImageGenerator::Result result = decoder->skipScanlines(linesToSkip);
+                SkCodec::Result result = decoder->skipScanlines(linesToSkip);
                 switch (result) {
-                    case SkImageGenerator::kSuccess:
-                    case SkImageGenerator::kIncompleteInput:
+                    case SkCodec::kSuccess:
+                    case SkCodec::kIncompleteInput:
                         break;
                     default:
                         return SkStringPrintf("Cannot skip scanlines for %s.", fPath.c_str());
@@ -311,8 +311,8 @@
                     result = decoder->getScanlines(bitmap.getAddr(0, startY),
                             linesToRead, bitmap.rowBytes());
                     switch (result) {
-                        case SkImageGenerator::kSuccess:
-                        case SkImageGenerator::kIncompleteInput:
+                        case SkCodec::kSuccess:
+                        case SkCodec::kIncompleteInput:
                             break;
                         default:
                             return SkStringPrintf("Cannot get scanlines for %s.", fPath.c_str());
@@ -329,11 +329,11 @@
                 // Read a stripe
                 const int startY = i * stripeHeight;
                 const int linesToRead = SkTMin(stripeHeight, height - startY);
-                SkImageGenerator::Result result = decoder->getScanlines(bitmap.getAddr(0, startY),
+                SkCodec::Result result = decoder->getScanlines(bitmap.getAddr(0, startY),
                         linesToRead, bitmap.rowBytes());
                 switch (result) {
-                    case SkImageGenerator::kSuccess:
-                    case SkImageGenerator::kIncompleteInput:
+                    case SkCodec::kSuccess:
+                    case SkCodec::kIncompleteInput:
                         break;
                     default:
                         return SkStringPrintf("Cannot get scanlines for %s.", fPath.c_str());
@@ -344,8 +344,8 @@
                 if (linesToSkip > 0) {
                     result = decoder->skipScanlines(linesToSkip);
                     switch (result) {
-                        case SkImageGenerator::kSuccess:
-                        case SkImageGenerator::kIncompleteInput:
+                        case SkCodec::kSuccess:
+                        case SkCodec::kIncompleteInput:
                             break;
                         default:
                             return SkStringPrintf("Cannot skip scanlines for %s.", fPath.c_str());