Reland again "Decode GIF image frames on demand".

Source/core/platform/graphics/chromium/DeferredImageDecoder.h

 /*
  * Copyright (C) 2012 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 43 matching lines @@
 
     ImageFrame* frameBufferAtIndex(size_t index);
 
     void setData(SharedBuffer* data, bool allDataReceived);
 
     bool isSizeAvailable();
     IntSize size() const;
     IntSize frameSizeAtIndex(size_t index) const;
     size_t frameCount();
     int repetitionCount() const;
-    void clearFrameBufferCache(size_t);
+    size_t clearCacheExceptFrame(size_t);
     bool frameHasAlphaAtIndex(size_t index) const;
     bool frameIsCompleteAtIndex(size_t) const;
     float frameDurationAtIndex(size_t) const;
     unsigned frameBytesAtIndex(size_t index) const;
     ImageOrientation orientation() const;
     bool hotSpot(IntPoint&) const;
 
 private:
     explicit DeferredImageDecoder(PassOwnPtr<ImageDecoder> actualDecoder);
     SkBitmap createLazyDecodingBitmap();
     void setData(PassRefPtr<SharedBuffer>, bool allDataReceived);
 
     RefPtr<SharedBuffer> m_data;
     bool m_allDataReceived;
     OwnPtr<ImageDecoder> m_actualDecoder;
 
     String m_filenameExtension;
     IntSize m_size;
     ImageOrientation m_orientation;
 
     ImageFrame m_lazyDecodedFrame;
     RefPtr<ImageFrameGenerator> m_frameGenerator;
 
     static bool s_enabled;
 };
 
 } // namespace WebCore
 
 #endif