Only paint the background onto the scrolling contents layer if we have a scrolling contents layer.

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 279 matching lines @@
     bool isolate = m_owningLayer.shouldIsolateCompositedDescendants();
 
     // non stacking context layers should never isolate
     ASSERT(m_owningLayer.stackingNode()->isStackingContext() || !isolate);
 
     m_graphicsLayer->setIsRootForIsolatedGroup(isolate);
 }
 
 void CompositedLayerMapping::updateBackgroundPaintsOntoScrollingContentsLayer()
 {
-    bool shouldPaintOntoScrollingContentsLayer = shouldPaintBackgroundOntoScrollingContentsLayer();
+    // We can only paint the background onto the scrolling contents layer if
+    // it would be visually correct and we are using composited scrolling meaning we
+    // have a scrolling contents layer to paint it into.
+    bool shouldPaintOntoScrollingContentsLayer =
+        canPaintBackgroundOntoScrollingContentsLayer()
+        && m_owningLayer.getScrollableArea()->usesCompositedScrolling();
     if (shouldPaintOntoScrollingContentsLayer != backgroundPaintsOntoScrollingContentsLayer()) {
         m_backgroundPaintsOntoScrollingContentsLayer = shouldPaintOntoScrollingContentsLayer;
         // If the background is no longer painted onto the scrolling contents
         // layer the scrolling contents layer needs to be updated. If it is
         // going to be painted onto the scrolling contents layer this update
         // will be triggered by LayoutBoxModelObject::setBackingNeedsPaintInvalidationInRect
         if (hasScrollingLayer() && !shouldPaintOntoScrollingContentsLayer)
             m_scrollingContentsLayer->setNeedsDisplay();
     }
 }
@@ skipping 2269 matching lines @@
         if (m_squashedLayers[previousIndex].paintLayer == layerToRemove)
             break;
     }
     if (previousIndex == indexToClear && layerToRemove->groupedMapping() == this) {
         compositor()->paintInvalidationOnCompositingChange(layerToRemove);
         return true;
     }
     return false;
 }
 
-bool CompositedLayerMapping::shouldPaintBackgroundOntoScrollingContentsLayer() const
+bool CompositedLayerMapping::canPaintBackgroundOntoScrollingContentsLayer() const
 {
     // TODO(flackr): Add support for painting locally attached background images. https://crbug.com/625882
     const FillLayer& backgroundLayer = m_owningLayer.layoutObject()->style()->backgroundLayers();
     return !m_owningLayer.isRootLayer()
         && m_owningLayer.scrollsOverflow()
         && !backgroundLayer.image()
         && !backgroundLayer.next()
         && (backgroundLayer.attachment() == LocalBackgroundAttachment
             || backgroundLayer.clip() == PaddingFillBox)
         && !m_owningLayer.stackingNode()->hasNegativeZOrderList();
@@ skipping 112 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink