Pull up initFrameBuffer to ImageDecoder.

third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 52 matching lines @@
                          size_t dataSize,
                          size_t frameIndex);
 
   WebPIDecoder* m_decoder;
   WebPDecBuffer m_decoderBuffer;
   int m_formatFlags;
   bool m_frameBackgroundHasAlpha;
 
   void readColorProfile();
   bool updateDemuxer();
-  bool initFrameBuffer(size_t frameIndex);
+
+  // Set |m_frameBackgroundHasAlpha| based on this frame's characteristics.
+  // Before calling this method, the caller must verify that the frame exists.
+  void onInitFrameBuffer(size_t frameIndex) override;
+
+  // When the blending method of this frame is BlendAtopPreviousFrame, the
+  // previous frame's buffer is necessary to decode this frame in
+  // applyPostProcessing, so we can't take over the data. Before calling this
+  // method, the caller must verify that the frame exists.
+  bool canReusePreviousFrameBuffer(size_t frameIndex) const override;
+
   void applyPostProcessing(size_t frameIndex);
   void clearFrameBuffer(size_t frameIndex) override;
 
   WebPDemuxer* m_demux;
   WebPDemuxState m_demuxState;
   bool m_haveAlreadyParsedThisData;
   int m_repetitionCount;
   int m_decodedHeight;
 
   typedef void (*AlphaBlendFunction)(ImageFrame&, ImageFrame&, int, int, int);
   AlphaBlendFunction m_blendFunction;
 
   void clear();
   void clearDecoder();
 
   // FIXME: Update libwebp's API so it does not require copying the data on each
   // update.
   sk_sp<SkData> m_consolidatedData;
 };
 
 }  // namespace blink
 
 #endif