Oilpan: fix build after r201436, r201444.

Source/web/InspectorOverlayImpl.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:
  *
  * 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
@@ skipping 143 matching lines @@
     ASSERT(!m_overlayPage);
 }
 
 DEFINE_TRACE(InspectorOverlayImpl)
 {
     visitor->trace(m_highlightNode);
     visitor->trace(m_eventTargetNode);
     visitor->trace(m_overlayPage);
     visitor->trace(m_overlayChromeClient);
     visitor->trace(m_overlayHost);
+    visitor->trace(m_debuggerAgent);
     visitor->trace(m_layoutEditor);
 }
 
 void InspectorOverlayImpl::init(InspectorCSSAgent* cssAgent, InspectorDebuggerAgent* debuggerAgent)
 {
     m_layoutEditor = LayoutEditor::create(cssAgent);
     m_debuggerAgent = debuggerAgent;
     m_overlayHost->setListener(this);
 }
 
@@ skipping 348 matching lines @@
     update();
 }
 
 void InspectorOverlayImpl::setShowViewportSizeOnResize(bool show, bool showGrid)
 {
     m_drawViewSize = show;
     m_drawViewSizeWithGrid = showGrid;
 }
 
 } // namespace blink