Decode GIF image frames on demand.

Source/core/platform/graphics/BitmapImage.h

 /*
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  *
  * 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 148 matching lines @@
     bool frameIsCompleteAtIndex(size_t);
     float frameDurationAtIndex(size_t);
     bool frameHasAlphaAtIndex(size_t);
     ImageOrientation frameOrientationAtIndex(size_t);
 
     // Decodes and caches a frame. Never accessed except internally.
     void cacheFrame(size_t index);
     // Called before accessing m_frames[index]. Returns false on index out of bounds.
     bool ensureFrameIsCached(size_t index);
 
-    // Called to invalidate cached data.  When |destroyAll| is true, we wipe out
-    // the entire frame buffer cache and tell the image source to destroy
-    // everything; this is used when e.g. we want to free some room in the image
-    // cache.  If |destroyAll| is false, we only delete frames up to the current
-    // one; this is used while animating large images to keep memory footprint
-    // low without redecoding the whole image on every frame.
-    virtual void destroyDecodedData(bool destroyAll = true);
+    // Called to invalidate cached data. This is used while animating large
+    // images to keep memory footprint low. The decoder may preserve some frames
+    // to avoid redecoding the whole image on every frame.
+    virtual void destroyDecodedData() OVERRIDE;

[Peter Kasting, 2013/05/29 02:02:18]

Nit: I'm a big fan of OVERRIDE, but if we're adding it to one function in this
file, perhaps we should add it to all.  (Applies to other files too)

[Xianzhu, 2013/05/29 18:37:01]

Done.

 
-    // If the image is large enough, calls destroyDecodedData() and passes
-    // |destroyAll| along.
-    void destroyDecodedDataIfNecessary(bool destroyAll);
+    // If the image is large enough, calls destroyDecodedData().
+    void destroyDecodedDataIfNecessary();
 
     // Generally called by destroyDecodedData(), destroys whole-image metadata
     // and notifies observers that the memory footprint has (hopefully)
     // decreased by |frameBytesCleared|.
-    void destroyMetadataAndNotify(unsigned frameBytesCleared);
+    void destroyMetadataAndNotify(size_t frameBytesCleared);
 
     // Whether or not size is available yet.    
     bool isSizeAvailable();
 
     // Called after asking the source for any information that may require
     // decoding part of the image (e.g., the image size).  We need to report
     // the partially decoded data to our observer so it has an accurate
     // account of the BitmapImage's memory usage.
     void didDecodeProperties() const;
 
@@ skipping 45 matching lines @@
     bool m_allDataReceived : 1; // Whether or not we've received all our data.
     mutable bool m_haveSize : 1; // Whether or not our |m_size| member variable has the final overall image size yet.
     bool m_sizeAvailable : 1; // Whether or not we can obtain the size of the first image frame yet from ImageIO.
     mutable bool m_hasUniformFrameSize : 1;
     mutable bool m_haveFrameCount : 1;
 };
 
 }
 
 #endif