Pull up clearCacheExceptFrame 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 32 matching lines @@
  public:
   WEBPImageDecoder(AlphaOption, ColorSpaceOption, size_t maxDecodedBytes);
   ~WEBPImageDecoder() override;
 
   // ImageDecoder:
   String filenameExtension() const override { return "webp"; }
   void onSetData(SegmentReader* data) override;
   int repetitionCount() const override;
   bool frameIsCompleteAtIndex(size_t) const override;
   float frameDurationAtIndex(size_t) const override;
-  size_t clearCacheExceptFrame(size_t) override;
 
  private:
   // ImageDecoder:
   virtual void decodeSize() { updateDemuxer(); }
   size_t decodeFrameCount() override;
   void initializeNewFrame(size_t) override;
   void decode(size_t) override;
 
   bool decodeSingleFrame(const uint8_t* dataBytes,
                          size_t dataSize,
                          size_t frameIndex);
 
+  // For WebP images, the frame status needs to be FrameComplete to decode
+  // subsequent frames that depend on frame |index|. The reason for this is that
+  // WebP uses the previous frame for alpha blending, in applyPostProcessing().
+  //
+  // Before calling this, verify that frame |index| exists by checking that
+  // |index| is smaller than |m_frameBufferCache|.size().
+  bool frameStatusSufficientForSuccessors(size_t index) override {
+    DCHECK(index < m_frameBufferCache.size());
+    return m_frameBufferCache[index].getStatus() == ImageFrame::FrameComplete;
+  }
+
   WebPIDecoder* m_decoder;
   WebPDecBuffer m_decoderBuffer;
   int m_formatFlags;
   bool m_frameBackgroundHasAlpha;
 
   void readColorProfile();
   bool updateDemuxer();
   bool initFrameBuffer(size_t frameIndex);
   void applyPostProcessing(size_t frameIndex);
   void clearFrameBuffer(size_t frameIndex) override;
@@ skipping 11 matching lines @@
   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