Use correct clip container when computing acl for scroll children

third_party/WebKit/Source/core/layout/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 790 matching lines @@
         scrollOrigin.move(-layoutBox->borderLeft(), -layoutBox->borderTop());
         graphicsLayerParentLocation = -(scrollOrigin + scrollOffset);
     }
 }
 
 void CompositedLayerMapping::updateAncestorClippingLayerGeometry(const PaintLayer* compositingContainer, const IntPoint& snappedOffsetFromCompositedAncestor, IntPoint& graphicsLayerParentLocation)
 {
     if (!compositingContainer || !m_ancestorClippingLayer)
         return;
 
+    if (scrollParent())
+        compositingContainer = scrollParent();
+
     ClipRectsContext clipRectsContext(compositingContainer, PaintingClipRectsIgnoringOverflowClip, IgnoreOverlayScrollbarSize);
     IntRect parentClipRect = pixelSnappedIntRect(m_owningLayer.clipper().backgroundClipRect(clipRectsContext).rect());
     ASSERT(parentClipRect != LayoutRect::infiniteIntRect());
     m_ancestorClippingLayer->setPosition(FloatPoint(parentClipRect.location() - graphicsLayerParentLocation));
     m_ancestorClippingLayer->setSize(FloatSize(parentClipRect.size()));
 
     // backgroundRect is relative to compositingContainer, so subtract snappedOffsetFromCompositedAncestor.X/snappedOffsetFromCompositedAncestor.Y to get back to local coords.
     m_ancestorClippingLayer->setOffsetFromLayoutObject(parentClipRect.location() - snappedOffsetFromCompositedAncestor);
 
     // The primary layer is then parented in, and positioned relative to this clipping layer.
@@ skipping 1756 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink