Oilpan: trace non-owned InspectorOverlay references.

Source/core/inspector/PageDebuggerAgent.cpp

 /*
  * Copyright (C) 2011 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 49 matching lines @@
 }
 
 PageDebuggerAgent::~PageDebuggerAgent()
 {
 }
 
 DEFINE_TRACE(PageDebuggerAgent)
 {
     visitor->trace(m_pageScriptDebugServer);
     visitor->trace(m_pageAgent);
+    visitor->trace(m_overlay);
     InspectorDebuggerAgent::trace(visitor);
 }
 
 void PageDebuggerAgent::enable()
 {
     InspectorDebuggerAgent::enable();
     m_instrumentingAgents->setPageDebuggerAgent(this);
 }
 
 void PageDebuggerAgent::disable()
@@ skipping 64 matching lines @@
 
 void PageDebuggerAgent::didClearDocumentOfWindowObject(LocalFrame* frame)
 {
     // FIXME: what about nested objects?
     if (frame != m_pageAgent->inspectedFrame())
         return;
     reset();
 }
 
 } // namespace blink
-