Add Blink APIs for frame tree mirroring.

public/web/WebRemoteFrame.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 WebRemoteFrame_h
 #define WebRemoteFrame_h
 
 #include "public/web/WebFrame.h"
 
 namespace blink {
 
 class WebRemoteFrame : public WebFrame {
 public:
     BLINK_EXPORT static WebRemoteFrame* create(WebFrameClient*);
+
+    virtual WebLocalFrame* createLocalChild(const WebString& name, WebFrameClient*) = 0;
+    virtual WebRemoteFrame* createRemoteChild(const WebString& name, WebFrameClient*) = 0;
 };
 
 } // namespace blink
 
 #endif // WebRemoteFrame_h