Introduce RenderFrameProxyHost object and use it in RFHM.

content/browser/frame_host/render_frame_proxy_host.h

Index: content/browser/frame_host/render_frame_proxy_host.h
diff --git a/content/browser/frame_host/render_frame_proxy_host.h b/content/browser/frame_host/render_frame_proxy_host.h
new file mode 100644
index 0000000000000000000000000000000000000000..994f79c38d47342085636338b0d53f1da89ab96e
--- /dev/null
+++ b/content/browser/frame_host/render_frame_proxy_host.h
@@ -0,0 +1,89 @@
+// 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"
+#include "content/browser/site_instance_impl.h"
+
+class RenderProcessHost;
+class RenderFrameHostImpl;
+class RenderViewHostImpl;
+
+namespace content {
+
+// When a page's frames are rendered by multiple processes, each renderer has a
+// full copy of the frame tree. It has full RenderFrames for the frames it is
+// responsible for rendering and placeholder objects (i.e., RenderFrameProxies)
+// for frames rendered by other processes.
+//
+// This class is the browser-side host object for the placeholder. Each node in
+// the frame tree has a RenderFrameHost for the active SiteInstance and a set
+// of RenderFrameProxyHost objects - one for all other SiteInstances with
+// references to this frame. The proxies allow us to keep existing window
+// references valid over cross-process navigations and route cross-site
+// asynchronous JavaScript calls, such as postMessage.
+//
+// For now, RenderFrameProxyHost is created when a RenderFrameHost is swapped
+// out and acts just as a wrapper. If a RenderFrameHost can be deleted, no
+// proxy object is created. It is destroyed when the RenderFrameHost is swapped
+// back in or is no longer referenced and is therefore deleted.
+//
+// Long term, RenderFrameProxyHost will be created whenever a cross-site
+// navigation occurs and a reference to the frame navigating needs to be kept
+// alive. A RenderFrameProxyHost and a RenderFrameHost for the same SiteInstance
+// can exist at the same time, but only one will be "active" at a time.
+// There are two cases where the two objects will coexist:
+// * When navigating cross-process and there is already a RenderFrameProxyHost
+// for the new SiteInstance. A pending RenderFrameHost is created, but it is
+// not used until it commits. At that point, RenderFrameHostManager transitions
+// the pending RenderFrameHost to the active one and deletes the proxy.
+// * When navigating cross-process and the existing document has an unload
+// event handler. When the new navigation commits, RenderFrameHostManager
+// creates a RenderFrameProxyHost for the old SiteInstance and uses it going
+// forward. It also instructs the RenderFrameHost to run the unload event
+// handler and is kept alive for the duration. Once the event handling is
+// complete, the RenderFrameHost is deleted.
+class RenderFrameProxyHost {
+ public:
+   RenderFrameProxyHost(
+       SiteInstanceImpl* site_instance,

[Charlie Reis, 2014/04/11 17:42:53]

Why not grab this from |render_frame_host| in the constructor for now, and skip
the |site_instance| parameter?  That prevents callers from ever passing a
mismatch.

[nasko, 2014/04/11 18:11:21]

Yeah, good idea. Tricky, but I think we are good.

+       scoped_ptr<RenderFrameHostImpl> render_frame_host);
+  ~RenderFrameProxyHost();
+
+  RenderProcessHost* GetProcess() {
+    return render_frame_host_->GetProcess();
+  }
+
+  SiteInstance* GetSiteInstance() {
+    return site_instance_.get();
+  }
+
+  // TODO(nasko): The following methods should be removed when swapping out
+  // of RenderFrameHosts is no longer used.
+  RenderFrameHostImpl* render_frame_host() {
+    return render_frame_host_.get();
+  }
+  RenderViewHostImpl* render_view_host() {
+    return render_frame_host_->render_view_host();
+  }
+  scoped_ptr<RenderFrameHostImpl> PassFrameHost() {
+    return render_frame_host_.Pass();
+  }
+
+ private:
+  scoped_refptr<SiteInstanceImpl> site_instance_;
+
+  // 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_