Decode GIF image frames on demand.

Source/core/platform/graphics/ImageSource.h

Index: Source/core/platform/graphics/ImageSource.h
diff --git a/Source/core/platform/graphics/ImageSource.h b/Source/core/platform/graphics/ImageSource.h
index 045232c03ac8fbabbc6ccfb93644580865139bc1..761df6518aef36caab5c5ba6ed32c3a11a3a6746 100644
--- a/Source/core/platform/graphics/ImageSource.h
+++ b/Source/core/platform/graphics/ImageSource.h
@@ -81,8 +81,8 @@ public:
     ~ImageSource();
 
     // Tells the ImageSource that the Image no longer cares about decoded frame
-    // data -- at all (if |destroyAll| is true), or before frame
-    // |clearBeforeFrame| (if |destroyAll| is false).  The ImageSource should
+    // data -- at all (if |destroyAll| is true), or except frame
+    // |clearExceptFrame| (if |destroyAll| is false). The ImageSource should
     // delete cached decoded data for these frames where possible to keep memory
     // usage low.  When |destroyAll| is true, the ImageSource should also reset
     // any local state so that decoding can begin again.
@@ -93,18 +93,11 @@ public:
     // asked to decode frames they can't decode due to the loss of previous
     // decoded frames.
     //
-    // Callers should not call clear(false, n) and subsequently call
-    // createFrameAtIndex(m) with m < n, unless they first call clear(true).
-    // This ensures that stateful ImageSources/decoders will work properly.
-    //
     // The |data| and |allDataReceived| parameters should be supplied by callers
     // who set |destroyAll| to true if they wish to be able to continue using
     // the ImageSource.  This way implementations which choose to destroy their
     // decoders in some cases can reconstruct them correctly.
-    void clear(bool destroyAll,
-               size_t clearBeforeFrame = 0,
-               SharedBuffer* data = NULL,
-               bool allDataReceived = false);
+    void clear(bool destroyAll, size_t clearExceptFrame = 0, SharedBuffer* data = 0, bool allDataReceived = false);
 
     bool initialized() const;