Oilpan: make shutdown of plugin container objects work better.

Source/platform/Widget.h

 /*
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) 2008 Collabora Ltd.  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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 115 matching lines @@
     virtual IntPoint convertToContainingView(const IntPoint&) const;
     virtual IntPoint convertFromContainingView(const IntPoint&) const;
 
     // Virtual methods to convert points to/from child widgets
     virtual IntPoint convertChildToSelf(const Widget*, const IntPoint&) const;
     virtual IntPoint convertSelfToChild(const Widget*, const IntPoint&) const;
 
     // Notifies this widget that it will no longer be receiving events.
     virtual void eventListenersRemoved() { }
 
+#if ENABLE(OILPAN)
+    virtual void detach() { }
+#endif
+
 private:
     Widget* m_parent;
     IntRect m_frame;
     bool m_selfVisible;
     bool m_parentVisible;
 };
 
 } // namespace WebCore
 
 #endif // Widget_h