Decode GIF image frames on demand.

Source/core/platform/graphics/BitmapImage.h

Index: Source/core/platform/graphics/BitmapImage.h
diff --git a/Source/core/platform/graphics/BitmapImage.h b/Source/core/platform/graphics/BitmapImage.h
index f4f17b28439bf079e592db8265c9d2a606f0c57b..d3906c9d4c11fc83facb02c624ae965b3d4b58b2 100644
--- a/Source/core/platform/graphics/BitmapImage.h
+++ b/Source/core/platform/graphics/BitmapImage.h
@@ -166,22 +166,18 @@ protected:
     // 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);
-
-    // If the image is large enough, calls destroyDecodedData() and passes
-    // |destroyAll| along.
-    void destroyDecodedDataIfNecessary(bool destroyAll);
+    // 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().
+    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();