Tried using CrossThreadPersistent for workerDebuggerAgents

Source/core/inspector/InspectorLayerTreeAgent.cpp

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 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.
@@ skipping 123 matching lines @@
     : InspectorBaseAgent<InspectorLayerTreeAgent>("LayerTree")
     , m_frontend(0)
     , m_page(page)
 {
 }
 
 InspectorLayerTreeAgent::~InspectorLayerTreeAgent()
 {
 }
 
+void InspectorLayerTreeAgent::trace(Visitor* visitor)
+{
+    visitor->trace(m_page);
+    InspectorBaseAgent::trace(visitor);
+}
+
 void InspectorLayerTreeAgent::setFrontend(InspectorFrontend* frontend)
 {
     m_frontend = frontend->layertree();
 }
 
 void InspectorLayerTreeAgent::clearFrontend()
 {
     m_frontend = 0;
     disable(0);
 }
@@ skipping 244 matching lines @@
 void InspectorLayerTreeAgent::didRemovePageOverlay(const GraphicsLayer* layer)
 {
     size_t index = m_pageOverlayLayerIds.find(layer->platformLayer()->id());
     if (index == WTF::kNotFound)
         return;
     m_pageOverlayLayerIds.remove(index);
 }
 
 
 } // namespace WebCore