Move the Widget hierarchy to the Oilpan heap.

Source/web/WebPluginScrollbarImpl.h

 /*
  * Copyright (C) 2012 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
  *     notice, this list of conditions and the following disclaimer in the
  *     documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
  * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (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 WebPluginScrollbarImpl_h
 #define WebPluginScrollbarImpl_h
 
+#include "platform/heap/Handle.h"
 #include "public/web/WebPluginScrollbar.h"
-
 #include "wtf/RefPtr.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class IntPoint;
 class IntRect;
 class Scrollbar;
 class ScrollbarGroup;
 
@@ skipping 45 matching lines @@
     bool onMouseUp(const WebInputEvent&);
     bool onMouseMove(const WebInputEvent&);
     bool onMouseLeave(const WebInputEvent&);
     bool onMouseWheel(const WebInputEvent&);
     bool onKeyDown(const WebInputEvent&);
 
     ScrollbarGroup* m_group;
     WebPluginScrollbarClient* m_client;
 
     int m_scrollOffset;
-    RefPtr<Scrollbar> m_scrollbar;
+    RefPtrWillBePersistent<Scrollbar> m_scrollbar;
 };
 
 } // namespace blink
 
 #endif