Reparented overflow controls host layer must account for scrolling.

Source/core/rendering/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 783 matching lines @@
             m_overflowControlsClippingLayer->setOffsetFromRenderer(m_ancestorClippingLayer->offsetFromRenderer());
             m_overflowControlsClippingLayer->setMasksToBounds(true);
 
             m_overflowControlsHostLayer->setPosition(IntPoint(-m_overflowControlsClippingLayer->offsetFromRenderer()));
         } else {
             // The controls are in the same 2D space as the compositing container, so we can map them into the space of the container.
             TransformState transformState(TransformState::ApplyTransformDirection, FloatPoint());
             m_owningLayer.renderer()->mapLocalToContainer(compositingStackingContext->renderer(), transformState, ApplyContainerFlip);
             transformState.flatten();
             LayoutPoint offsetFromStackingContainer = LayoutPoint(transformState.lastPlanarPoint());
+            if (RenderLayerScrollableArea* scrollableArea = compositingStackingContext->scrollableArea())
+                offsetFromStackingContainer.move(LayoutSize(scrollableArea->adjustedScrollOffset()));
             m_overflowControlsHostLayer->setPosition(FloatPoint(offsetFromStackingContainer));
         }
     } else {
         m_overflowControlsHostLayer->setPosition(FloatPoint());
     }
 }
 
 void CompositedLayerMapping::updateChildContainmentLayerGeometry(const IntRect& clippingBox, const IntRect& localCompositingBounds)
 {
     if (!m_childContainmentLayer)
@@ skipping 1510 matching lines @@
     } else if (graphicsLayer == m_scrollingBlockSelectionLayer.get()) {
         name = "Scrolling Block Selection Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink