Plumb an overscroll callback form the compositor to the Android UI thread.

cc/compositor_frame_metadata.h

Index: cc/compositor_frame_metadata.h
diff --git a/cc/compositor_frame_metadata.h b/cc/compositor_frame_metadata.h
index 5d9a9056a1e61298a1bd2b3d088cc52ff61c4bc4..bbf3de4bc500b7d38cc0598d4e5e6731146f681a 100644
--- a/cc/compositor_frame_metadata.h
+++ b/cc/compositor_frame_metadata.h
@@ -33,6 +33,9 @@ class CC_EXPORT CompositorFrameMetadata
   // precise position is computed by the renderer compositor.
   gfx::Vector2dF location_bar_offset;
   gfx::Vector2dF location_bar_content_translation;
+
+  // The amount scroll delta that was unused.

[aelias_OOO_until_Jul13, 2013/01/30 18:02:48]

Mention this is for Android overscroll.

+  gfx::Vector2dF unused_scroll_delta;
 };
 
 }  // namespace cc