Reland again "Decode GIF image frames on demand".

Source/core/platform/graphics/ImageSource.cpp

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp.toker@collabora.co.uk>
  * Copyright (C) 2008, 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.
@@ skipping 27 matching lines @@
 namespace WebCore {
 
 ImageSource::ImageSource(ImageSource::AlphaOption alphaOption, ImageSource::GammaAndColorProfileOption gammaAndColorProfileOption)
     : m_alphaOption(alphaOption)
     , m_gammaAndColorProfileOption(gammaAndColorProfileOption)
 {
 }
 
 ImageSource::~ImageSource()
 {
-    clear(true);
 }
 
-void ImageSource::clear(bool destroyAll, size_t clearBeforeFrame, SharedBuffer* data, bool allDataReceived)
+size_t ImageSource::clearCacheExceptFrame(size_t clearExceptFrame)
 {
-    if (!destroyAll) {
-        if (m_decoder)
-            m_decoder->clearFrameBufferCache(clearBeforeFrame);
-        return;
-    }
-
-    m_decoder.clear();
-    if (data)
-        setData(data, allDataReceived);
+    return m_decoder ? m_decoder->clearCacheExceptFrame(clearExceptFrame) : 0;
 }
 
 bool ImageSource::initialized() const
 {
     return m_decoder;
 }
 
 void ImageSource::setData(SharedBuffer* data, bool allDataReceived)
 {
     // Make the decoder by sniffing the bytes.
@@ skipping 110 matching lines @@
     return m_decoder->frameBytesAtIndex(index);
 }
 
 void ImageSource::reportMemoryUsage(MemoryObjectInfo* memoryObjectInfo) const
 {
     MemoryClassInfo info(memoryObjectInfo, this, PlatformMemoryTypes::Image);
     info.addMember(m_decoder, "decoder");
 }
 
 }