Move the Widget hierarchy to the Oilpan heap.

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 13 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef Widget_h
 #define Widget_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatPoint.h"
 #include "platform/geometry/IntRect.h"
+#include "platform/heap/Handle.h"
 #include "wtf/Forward.h"
 #include "wtf/RefCounted.h"
 
 namespace blink {
 
 class Event;
 class GraphicsContext;
 class HostWindow;
 
 // The Widget class serves as a base class for three kinds of objects:
 // (1) Scrollable areas (ScrollView)
 // (2) Scrollbars (Scrollbar)
 // (3) Plugins (PluginView)
 //
 // Widgets are connected in a hierarchy, with the restriction that plugins and
 // scrollbars are always leaves of the tree. Only ScrollViews can have children
 // (and therefore the Widget class has no concept of children).
-class PLATFORM_EXPORT Widget : public RefCounted<Widget> {
+class PLATFORM_EXPORT Widget : public RefCountedWillBeGarbageCollectedFinalized<Widget> {
 public:
     Widget();
     virtual ~Widget();
 
     int x() const { return frameRect().x(); }
     int y() const { return frameRect().y(); }
     int width() const { return frameRect().width(); }
     int height() const { return frameRect().height(); }
     IntSize size() const { return frameRect().size(); }
     IntPoint location() const { return frameRect().location(); }
@@ skipping 58 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
+    virtual void trace(Visitor*);
 
 private:
-    Widget* m_parent;
+    RawPtrWillBeMember<Widget> m_parent;
     IntRect m_frame;
     bool m_selfVisible;
     bool m_parentVisible;
 };
 
 } // namespace blink
 
 #endif // Widget_h