Introduce RenderFrameProxyHost object and use it in RFHM.

content/browser/frame_host/render_frame_proxy_host.cc

+// 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.
+
+#include "content/browser/frame_host/render_frame_proxy_host.h"
+
+#include "content/browser/frame_host/render_frame_host_impl.h"
+#include "content/browser/site_instance_impl.h"
+
+namespace content {
+
+RenderFrameProxyHost::RenderFrameProxyHost(
+    scoped_ptr<RenderFrameHostImpl> render_frame_host)
+    : site_instance_(render_frame_host->GetSiteInstance()),
+      render_frame_host_(render_frame_host.Pass()) {}
+
+RenderFrameProxyHost::~RenderFrameProxyHost() {}
+
+}  // namespace content