Pull up initFrameBuffer to ImageDecoder.

third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.h

Index: third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.h
diff --git a/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.h b/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.h
index 1987dfcf306d75878c83a6487451f608b9ad3f5c..85151371244dd55c150b8dc6e8cdcac521e52b7f 100644
--- a/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.h
+++ b/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.h
@@ -82,10 +82,16 @@ class PLATFORM_EXPORT GIFImageDecoder final : public ImageDecoder {
   // data. If parsing fails, sets the "decode failure" flag.
   void parse(GIFParseQuery);
 
-  // Called to initialize the frame buffer with the given index, based on
-  // the previous frame's disposal method. Returns true on success. On
-  // failure, this will mark the image as failed.
-  bool initFrameBuffer(size_t frameIndex);
+  // In addition to ImageDecoder::initFrameBuffer, also reset the alpha tracker
+  // for this frame. Before calling this method, the callee must verify that

[scroggo_chromium, 2016/11/14 13:51:46]

caller*

[joostouwerling, 2016/11/14 16:25:10]

Done.

+  // the frame exists.
+  bool initFrameBuffer(size_t) override;
+
+  // When the disposal method of the frame is DisposeOverWritePrevious, the
+  // next frame will use the previous frame's buffer as its starting state, so
+  // we can't take over the data in that case. Before calling this method, the
+  // callee must verify that the frame exists.

[scroggo_chromium, 2016/11/14 13:51:46]

caller*

[joostouwerling, 2016/11/14 16:25:10]

Done.

+  bool canReusePreviousFrameBuffer(size_t) const override;
 
   // Like clearCacheExceptFrame(), but preserves two frames instead of one.
   size_t clearCacheExceptTwoFrames(size_t, size_t);