+ // This layer exists to simplify the reparenting of overflow control that is occasionally required
+ // to ensure that scrollbars appear above scrolling content.
+ OwnPtr<GraphicsLayer> m_overflowControlsHostLayer;
+
+ // The reparented overflow controls sometimes need to be clipped by a non-ancestor. In just the same
+ // way we need an ancestor clipping layer to clip this CLM's internal hierarchy, we add another layer
+ // to clip the overflow controls. It would be possible to make m_overflowControlsHostLayer be
+ // responsible for applying this clip, but that could require repositioning all of the overflow
+ // controls since the this clip may apply an offset. By using a separate layer, the overflow controls
+ // can remain ignorant of the layers above them and still work correctly.
+ OwnPtr<GraphicsLayer> m_overflowControlsClippingLayer;
+