Move the Widget hierarchy to the Oilpan heap.

Source/core/html/HTMLPlugInElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 27 matching lines @@
 
 enum PreferPlugInsForImagesOption {
     ShouldPreferPlugInsForImages,
     ShouldNotPreferPlugInsForImages
 };
 
 class HTMLPlugInElement : public HTMLFrameOwnerElement {
 public:
     virtual ~HTMLPlugInElement();
     virtual void trace(Visitor*) override;
+#if ENABLE(OILPAN)
+    virtual void disconnectContentFrame() override;
+#endif
 
     void resetInstance();
     SharedPersistent<v8::Object>* pluginWrapper();
     Widget* pluginWidget() const;
     NPObject* getNPObject();
     bool canProcessDrag() const;
     const String& url() const { return m_url; }
 
     // Public for FrameView::addWidgetToUpdate()
     bool needsWidgetUpdate() const { return m_needsWidgetUpdate; }
@@ skipping 66 matching lines @@
 
     // Return any existing RenderWidget without triggering relayout, or 0 if it
     // doesn't yet exist.
     virtual RenderWidget* existingRenderWidget() const = 0;
     virtual void updateWidgetInternal() = 0;
 
     bool loadPlugin(const KURL&, const String& mimeType, const Vector<String>& paramNames, const Vector<String>& paramValues, bool useFallback, bool requireRenderer);
     bool pluginIsLoadable(const KURL&, const String& mimeType);
     bool wouldLoadAsNetscapePlugin(const String& url, const String& serviceType);
 
+    void setPersistedPluginWidget(Widget*);
+
     mutable RefPtr<SharedPersistent<v8::Object> > m_pluginWrapper;
     NPObject* m_NPObject;
     bool m_isCapturingMouseEvents;
     bool m_needsWidgetUpdate;
     bool m_shouldPreferPlugInsForImages;
     bool m_usePlaceholderContent;
 
     // Normally the Widget is stored in HTMLFrameOwnerElement::m_widget.
     // However, plugins can persist even when not rendered. In order to
     // prevent confusing code which may assume that widget() != null
     // means the frame is active, we save off m_widget here while
     // the plugin is persisting but not being displayed.
-    RefPtr<Widget> m_persistedPluginWidget;
+    RefPtrWillBeMember<Widget> m_persistedPluginWidget;
 };
 
 inline bool isHTMLPlugInElement(const HTMLElement& element)
 {
     return element.isPluginElement();
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLPlugInElement);
 
 } // namespace blink
 
 #endif // HTMLPlugInElement_h