Cache image data objects.

ppapi/thunk/ppb_graphics_2d_api.h

Index: ppapi/thunk/ppb_graphics_2d_api.h
diff --git a/ppapi/thunk/ppb_graphics_2d_api.h b/ppapi/thunk/ppb_graphics_2d_api.h
index 80c8c78f272fd51aa129dba2ddfff6c4bba149f7..f0b76765d1e05868380acf9e188a32187badc08b 100644
--- a/ppapi/thunk/ppb_graphics_2d_api.h
+++ b/ppapi/thunk/ppb_graphics_2d_api.h
@@ -27,9 +27,17 @@ class PPB_Graphics2D_API {
   virtual void Scroll(const PP_Rect* clip_rect,
                       const PP_Point* amount) = 0;
   virtual void ReplaceContents(PP_Resource image_data) = 0;
-  virtual int32_t Flush(scoped_refptr<TrackedCallback> callback) = 0;
   virtual bool SetScale(float scale) = 0;
   virtual float GetScale() = 0;
+
+  // When |*old_image_data| is non-null and the flush is executing a replace

[yzshen1, 2012/08/21 22:07:24]

nit: |*old_image_data| looks like "deref old_image_data", so the first and the
third |*old_image_data| are better changed to |old_image_data|.

+  // contents (which leaves the "old" ImageData unowned), the resource ID of
+  // the old image data will be placed into |*old_image_data|. A reference to
+  // this resource will be transferred to the caller. If there is no replace
+  // contents operation, old_image_data will be ignored. If |*old_image_data|
+  // is null, then the old image data will be destroyed if there was one.
+  virtual int32_t Flush(scoped_refptr<TrackedCallback> callback,
+                        PP_Resource* old_image_data) = 0;

[yzshen1, 2012/08/21 22:07:24]

Please comment that |old_image_data| is used 'synchronously'. It can be freed as
soon as this method returns.

 };
 
 }  // namespace thunk