Move the Widget hierarchy to the Oilpan heap.

Source/core/frame/RemoteFrameView.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef RemoteFrameView_h
 #define RemoteFrameView_h
 
 #include "platform/Widget.h"
 #include "platform/geometry/IntRect.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class RemoteFrame;
 
-class RemoteFrameView : public Widget {
+class RemoteFrameView final : public Widget {
 public:
-    static PassRefPtr<RemoteFrameView> create(RemoteFrame*);
+    static PassRefPtrWillBeRawPtr<RemoteFrameView> create(RemoteFrame*);
 
     virtual ~RemoteFrameView();
 
     virtual bool isRemoteFrameView() const override { return true; }
 
     RemoteFrame& frame() const
     {
         ASSERT(m_remoteFrame);
         return *m_remoteFrame;
     }
 
     // Override to notify remote frame that its viewport size has changed.
     virtual void frameRectsChanged() override;
 
     virtual void invalidateRect(const IntRect&) override;
 
     virtual void setFrameRect(const IntRect&) override;
 
+    virtual void trace(Visitor*) override;
+
 private:
     explicit RemoteFrameView(RemoteFrame*);
 
-    // The RefPtrWillBePersistent-cycle between RemoteFrame and its RemoteFrameView
-    // is broken in the same manner as FrameView::m_frame and LocalFrame::m_view is.
-    // See the FrameView::m_frame comment.
-    RefPtrWillBePersistent<RemoteFrame> m_remoteFrame;
+    // The properties and handling of the cycle between RemoteFrame
+    // and its RemoteFrameView corresponds to that between LocalFrame
+    // and FrameView. Please see the FrameView::m_frame comment for
+    // details.
+    RefPtrWillBeMember<RemoteFrame> m_remoteFrame;
 };
 
 DEFINE_TYPE_CASTS(RemoteFrameView, Widget, widget, widget->isRemoteFrameView(), widget.isRemoteFrameView());
 
 } // namespace blink
 
 #endif // RemoteFrameView_h