Option for SkCodec to treat dst as all zeroes.

This recreates SkImageDecoder's feature to skip writing zeroes for
SkCodec.

Review URL: https://codereview.chromium.org/980903002
diff --git a/src/codec/SkCodec_libbmp.cpp b/src/codec/SkCodec_libbmp.cpp
index 5b9691c..a96cd66 100644
--- a/src/codec/SkCodec_libbmp.cpp
+++ b/src/codec/SkCodec_libbmp.cpp
@@ -502,6 +502,7 @@
  */
 SkCodec::Result SkBmpCodec::onGetPixels(const SkImageInfo& dstInfo,
                                         void* dst, size_t dstRowBytes,
+                                        const Options&,
                                         SkPMColor*, int*) {
     if (!this->rewindIfNeeded()) {
         return kCouldNotRewind;
@@ -844,7 +845,7 @@
 
     // Create swizzler
     SkSwizzler* swizzler = SkSwizzler::CreateSwizzler(config, fColorTable.get(),
-            dstInfo, dst, dstRowBytes, false);
+            dstInfo, dst, dstRowBytes, SkImageGenerator::kNo_ZeroInitialized);
 
     // Allocate space for a row buffer and a source for the swizzler
     SkAutoTDeleteArray<uint8_t> srcBuffer(SkNEW_ARRAY(uint8_t, rowBytes));