Add a basic DOMWindow base class and use it in WindowProxy.

Source/core/frame/RemoteFrame.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 RemoteFrame_h
 #define RemoteFrame_h
 
 #include "core/frame/Frame.h"
 
 namespace blink {
 
 class Event;
 class RemoteFrameClient;
 class RemoteFrameView;
 
 class RemoteFrame: public Frame {
 public:
     static PassRefPtrWillBeRawPtr<RemoteFrame> create(RemoteFrameClient*, FrameHost*, FrameOwner*);
-    virtual bool isRemoteFrame() const override { return true; }
 
     virtual ~RemoteFrame();
 
+    // Frame overrides:
+    void trace(Visitor*) override;
+    virtual bool isRemoteFrame() const override { return true; }
+    virtual LocalDOMWindow* domWindow() const override { return 0; }
     virtual void navigate(Document& originDocument, const KURL&, bool lockBackForwardList) override;
     virtual void detach() override;
 
     // FIXME: Remove this method once we have input routing in the browser
     // process. See http://crbug.com/339659.
     void forwardInputEvent(Event*);
 
     void setView(PassRefPtrWillBeRawPtr<RemoteFrameView>);
     void createView();
 
     RemoteFrameView* view() const;
 
-    void trace(Visitor*) override;
 
 private:
     RemoteFrame(RemoteFrameClient*, FrameHost*, FrameOwner*);
 
     RemoteFrameClient* remoteFrameClient() const;
 
     RefPtrWillBeMember<RemoteFrameView> m_view;
 };
 
 inline RemoteFrameView* RemoteFrame::view() const
 {
     return m_view.get();
 }
 
 DEFINE_TYPE_CASTS(RemoteFrame, Frame, remoteFrame, remoteFrame->isRemoteFrame(), remoteFrame.isRemoteFrame());
 
 } // namespace blink
 
 #endif // RemoteFrame_h