Ensure that we consistently check contains: paint for fixed position containment.

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 1085 matching lines @@
     // Register fixed position layers and their containers with the scrolling coordinator.
     ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer);
     if (!scrollingCoordinator)
         return;
 
     scrollingCoordinator->updateLayerPositionConstraint(&m_owningLayer);
 
     // Page scale is applied as a transform on the root layout view layer. Because the scroll
     // layer is further up in the hierarchy, we need to avoid marking the root layout view
     // layer as a container.
-    bool isContainer = m_owningLayer.hasTransformRelatedProperty() && !m_owningLayer.isRootLayer();
+    bool isContainer = m_owningLayer.layoutObject()->style()->canContainFixedPositionObjects() && !m_owningLayer.isRootLayer();
     // FIXME: we should make certain that childForSuperLayers will never be the m_squashingContainmentLayer here
     scrollingCoordinator->setLayerIsContainerForFixedPositionLayers(childForSuperlayers(), isContainer);
 }
 
 void CompositedLayerMapping::updateInternalHierarchy()
 {
     // m_foregroundLayer has to be inserted in the correct order with child layers,
     // so it's not inserted here.
     if (m_ancestorClippingLayer)
         m_ancestorClippingLayer->removeAllChildren();
@@ skipping 1552 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink