Pull up initFrameBuffer to ImageDecoder.

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

Index: third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.h
diff --git a/third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.h b/third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.h
index 2800775cf773aeed9093fa784802505b7ba94530..7e64ddc707744aa2096c17674eff8d04ebf17a30 100644
--- a/third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.h
+++ b/third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.h
@@ -70,7 +70,18 @@ class PLATFORM_EXPORT WEBPImageDecoder final : public ImageDecoder {
 
   void readColorProfile();
   bool updateDemuxer();
-  bool initFrameBuffer(size_t frameIndex);
+
+  // In addition to ImageDecoder::initFrameBuffer, also set
+  // |m_frameBackgroundHasAlpha| based on this frame's characteristics. 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 initFrameBuffer(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 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 frameIndex) const override;
+
   void applyPostProcessing(size_t frameIndex);
   void clearFrameBuffer(size_t frameIndex) override;