Refactor fixed layout mode

Source/core/rendering/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 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 1275 matching lines @@
         !!fixedRootBackgroundLayer()
             ? ScrolledMainFrameWithAcceleratedFixedRootBackground
             : ScrolledMainFrameWithUnacceleratedFixedRootBackground,
         AcceleratedFixedRootBackgroundHistogramMax);
 }
 
 void RenderLayerCompositor::frameViewDidLayout()
 {
 }
 
+void RenderLayerCompositor::frameViewScrollbarsExistenceDidChange()
+{
+    if (m_containerLayer)
+        updateOverflowControlsLayers();
+}
+
 void RenderLayerCompositor::rootFixedBackgroundsChanged()
 {
     if (!supportsFixedRootBackgroundCompositing())
         return;
 
     // To avoid having to make the fixed root background layer fixed positioned to
     // stay put, we position it in the layer tree as follows:
     //
     // + Overflow controls host
     //   + Frame clip
@@ skipping 1482 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "Frame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore