Add a WebRemoteFrameClient interface to public/web

public/web/WebRemoteFrameClient.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 WebRemoteFrameClient_h
+#define WebRemoteFrameClient_h
+
+#include "public/web/WebFrameClient.h"
+
+namespace blink {
+
+class WebRemoteFrameClient : public WebFrameClient {

[Nate Chapin, 2014/09/04 23:16:48]

This inheritance is temporary. Once RenderFrameProxy inherits from
WebRemoteFrameClient instead of WebFrameClient, WebRemoteFrame can be update to
take a WebRemoteFrameClient in its constructor.

+public:
+    // Notifies the embedder that a postMessage was issued to a remote frame.
+    virtual void postMessageEvent(
+        WebLocalFrame* sourceFrame,
+        WebRemoteFrame* targetFrame,
+        WebSecurityOrigin targetOrigin,
+        WebDOMMessageEvent) = 0;
+};
+
+} // namespace blink
+
+#endif // WebRemoteFrameClient_h