[DevTools] Use WebLayerTreeView::layerTreeId() for instrumentation.

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 926 matching lines @@
     return document->focusedElement();
 }
 
 void WebFrameWidgetImpl::initializeLayerTreeView()
 {
     if (m_client) {
         m_client->initializeLayerTreeView();
         m_layerTreeView = m_client->layerTreeView();
     }
 
+    if (WebDevToolsAgentImpl* devTools = m_localRoot->devToolsAgentImpl())
+        devTools->layerTreeViewChanged(m_layerTreeView);
+
     m_page->settings().setAcceleratedCompositingEnabled(m_layerTreeView);
 
     // FIXME: only unittests, click to play, Android priting, and printing (for headers and footers)
     // make this assert necessary. We should make them not hit this code and then delete allowsBrokenNullLayerTreeView.
     ASSERT(m_layerTreeView || !m_client || m_client->allowsBrokenNullLayerTreeView());
 }
 
 void WebFrameWidgetImpl::setIsAcceleratedCompositingActive(bool active)
 {
     // In the middle of shutting down; don't try to spin back up a compositor.
@@ skipping 90 matching lines @@
     // correspond to Page visibility, but is necessary until we properly sort out OOPIF visibility.
     m_page->setVisibilityState(static_cast<PageVisibilityState>(visibilityState), isInitialState);
 
     if (m_layerTreeView) {
         bool visible = visibilityState == WebPageVisibilityStateVisible;
         m_layerTreeView->setVisible(visible);
     }
 }
 
 } // namespace blink