Introduce RenderFrameProxyHost object and use it in RFHM.

content/browser/frame_host/render_frame_proxy_host.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 CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_PROXY_HOST_H_
+#define CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_PROXY_HOST_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "content/browser/frame_host/render_frame_host_impl.h"
+
+class RenderProcessHost;
+class RenderFrameHostImpl;
+class RenderViewHostImpl;
+
+namespace content {
+
+class RenderFrameProxyHost {

[Charlie Reis, 2014/03/31 23:22:35]

This class needs a big helpful comment.  Some things to cover:
 - Each renderer process with a reference to this frame (other than the one
rendering it) has a RenderFrameProxy placeholder for it.
 - This is the browser-side part of that placeholder.
 - The placeholder allows us to keep existing window references valid and route
cross-process JS calls like postMessage.
 - Lifetime (for now): Created when RFH swapped out, deleted when swapped back
in or unreferenced
 - Lifetime (planned): RFH and RFPH live at mutually exclusive times (apart from
waiting for RFH to unload and exit?)

[nasko, 2014/04/09 17:52:01]

Done.

+ public:
+   explicit RenderFrameProxyHost(
+       scoped_ptr<RenderFrameHostImpl> render_frame_host);
+  ~RenderFrameProxyHost();
+
+  RenderProcessHost* GetProcess() {
+    DCHECK(render_frame_host_.get());

[Charlie Reis, 2014/03/31 23:22:35]

This is kind of redundant, since we'll crash on the next line anyway if it's
null.

[nasko, 2014/04/09 17:52:01]

Done.

+    return render_frame_host_->GetProcess();
+  }
+  RenderFrameHostImpl* render_frame_host() {
+    return render_frame_host_.get();
+  }
+  RenderViewHostImpl* render_view_host() {
+    if (render_frame_host_)

[Charlie Reis, 2014/03/31 23:22:35]

When is this not null?  Does the RFPH ever outlive its reference to the RFH?

[nasko, 2014/04/09 17:52:01]

Done.

+      return render_frame_host_->render_view_host();
+    return NULL;
+  }
+  scoped_ptr<RenderFrameHostImpl> PassFrameHost() {
+    return render_frame_host_.Pass();
+  }
+
+ private:
+
+  // TODO(nasko): For now, hide the RenderFrameHost inside the proxy, but remove
+  // it once we have all the code support for proper proxy objects.
+  scoped_ptr<RenderFrameHostImpl> render_frame_host_;
+
+  DISALLOW_COPY_AND_ASSIGN(RenderFrameProxyHost);
+};
+
+}  // namespace
+
+#endif  // CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_PROXY_HOST_H_