Refactor the way PaintArtifactCompositor is attached and used.

third_party/WebKit/Source/web/WebFrameWidgetImpl.cpp

 /*
  * Copyright (C) 2014 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 1342 matching lines @@
 
     if (!m_layerTreeView)
         return;
 
     if (m_rootLayer)
         m_layerTreeView->setRootLayer(*m_rootLayer);
     else
         m_layerTreeView->clearRootLayer();
 }
 
+void WebFrameWidgetImpl::setRootLayer(WebLayer* layer)
+{
+    m_rootLayer = layer;
+
+    setIsAcceleratedCompositingActive(layer);
+
+    if (!m_layerTreeView)
+        return;
+
+    if (m_rootLayer)
+        m_layerTreeView->setRootLayer(*m_rootLayer);
+    else
+        m_layerTreeView->clearRootLayer();
+}
+
 void WebFrameWidgetImpl::attachCompositorAnimationTimeline(CompositorAnimationTimeline* compositorTimeline)
 {
     if (m_layerTreeView)
         m_layerTreeView->attachCompositorAnimationTimeline(compositorTimeline->animationTimeline());
 
 }
 
 void WebFrameWidgetImpl::detachCompositorAnimationTimeline(CompositorAnimationTimeline* compositorTimeline)
 {
     if (m_layerTreeView)
@@ skipping 105 matching lines @@
 }
 
 LocalFrame* WebFrameWidgetImpl::focusedLocalFrameAvailableForIme() const
 {
     if (!m_imeAcceptEvents)
         return nullptr;
     return focusedLocalFrameInWidget();
 }
 
 } // namespace blink