Reland again "Decode GIF image frames on demand".

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

 /*
  * 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 153 matching lines @@
 size_t DeferredImageDecoder::frameCount()
 {
     return m_actualDecoder ? m_actualDecoder->frameCount() : 1;
 }
 
 int DeferredImageDecoder::repetitionCount() const
 {
     return m_actualDecoder ? m_actualDecoder->repetitionCount() : cAnimationNone;
 }
 
-void DeferredImageDecoder::clearFrameBufferCache(size_t clearBeforeFrame)
+size_t DeferredImageDecoder::clearCacheExceptFrame(size_t clearExceptFrame)
 {
     // If image decoding is deferred then frame buffer cache is managed by
     // the compositor and this call is ignored.
-    if (m_actualDecoder)
-        m_actualDecoder->clearFrameBufferCache(clearBeforeFrame);
+    return m_actualDecoder ? m_actualDecoder->clearCacheExceptFrame(clearExceptFrame) : 0;
 }
 
 bool DeferredImageDecoder::frameHasAlphaAtIndex(size_t index) const
 {
     return m_actualDecoder ? m_actualDecoder->frameHasAlphaAtIndex(index) : m_frameGenerator->hasAlpha();
 }
 
 bool DeferredImageDecoder::frameIsCompleteAtIndex(size_t index) const
 {
     // TODO: Implement this for deferred decoding.
@@ skipping 48 matching lines @@
 
     return bitmap;
 }
 
 bool DeferredImageDecoder::hotSpot(IntPoint& hotSpot) const
 {
     return m_actualDecoder ? m_actualDecoder->hotSpot(hotSpot) : false;
 }
 
 } // namespace WebCore