Optimization for image decoding using Skia discardable memory

Source/platform/graphics/ImageFrameGenerator.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 68 matching lines @@
     void copyData(RefPtr<SharedBuffer>*, bool* allDataReceived);
 
     SkISize getFullSize() const { return m_fullSize; }
 
     bool isMultiFrame() const { return m_isMultiFrame; }
 
     // FIXME: Return alpha state for each frame.
     bool hasAlpha(size_t);
 
 private:
+    class ExternalMemoryAllocator;
     friend class ImageFrameGeneratorTest;
     friend class DeferredImageDecoderTest;
     // For testing. |factory| will overwrite the default ImageDecoder creation logic if |factory->create()| returns non-zero.
     void setImageDecoderFactory(PassOwnPtr<ImageDecoderFactory> factory) { m_imageDecoderFactory = factory; }
     // For testing.
-    SkBitmap::Allocator* allocator() const { return m_allocator.get(); }
-    void setAllocator(PassOwnPtr<SkBitmap::Allocator> allocator) { m_allocator = allocator; }
+    SkBitmap::Allocator* allocator() const { return m_discardableAllocator.get(); }
+    void setAllocator(PassOwnPtr<SkBitmap::Allocator> allocator) { m_discardableAllocator = allocator; }
 
     // These methods are called while m_decodeMutex is locked.
     const ScaledImageFragment* tryToLockCompleteCache(const SkISize& scaledSize, size_t index);
     const ScaledImageFragment* tryToResumeDecode(const SkISize& scaledSize, size_t index);
 
     // Use the given decoder to decode. If a decoder is not given then try to create one.
     PassOwnPtr<ScaledImageFragment> decode(size_t index, ImageDecoder**);
 
     // Return the next generation ID of a new image object. This is used
     // to identify images of the same frame from different stages of
     // progressive decode.
     size_t nextGenerationId() { return m_decodeCount++; }
 
     SkISize m_fullSize;
     ThreadSafeDataTransport m_data;
     bool m_isMultiFrame;
     bool m_decodeFailedAndEmpty;
     Vector<bool> m_hasAlpha;
     size_t m_decodeCount;
-    OwnPtr<SkBitmap::Allocator> m_allocator;
+    OwnPtr<SkBitmap::Allocator> m_discardableAllocator;
+    OwnPtr<ExternalMemoryAllocator> m_externalAllocator;
 
     OwnPtr<ImageDecoderFactory> m_imageDecoderFactory;
 
     // Prevents multiple decode operations on the same data.
     Mutex m_decodeMutex;
 
     // Protect concurrent access to m_hasAlpha.
     Mutex m_alphaMutex;
 };
 
 } // namespace WebCore
 
 #endif