Fix issue when background changes painting target 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 350 matching lines @@
   // 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 =
       m_owningLayer.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)
+    // The scrolling contents layer needs to be updated for changed
+    // m_backgroundPaintsOntoScrollingContentsLayer.
+    if (hasScrollingLayer())
       m_scrollingContentsLayer->setNeedsDisplay();
   }
 }
 
 void CompositedLayerMapping::updateContentsOpaque() {
   if (isAcceleratedCanvas(layoutObject())) {
     // Determine whether the rendering context's external texture layer is
     // opaque.
     CanvasRenderingContext* context =
         toHTMLCanvasElement(layoutObject()->node())->renderingContext();
@@ skipping 2865 matching lines @@
   } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
     name = "Scrolling Contents Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink