Prerendered pages are swapped in at browser::Navigate time.

chrome/common/prerender_messages.h

Index: chrome/common/prerender_messages.h
diff --git a/chrome/common/prerender_messages.h b/chrome/common/prerender_messages.h
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+// Copyright (c) 2012 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.
+
+// Multiply-included message file, no traditional include guard.
+#include "googleurl/src/gurl.h"
+#include "ipc/ipc_message.h"
+#include "ipc/ipc_message_macros.h"
+#include "ipc/ipc_param_traits.h"
+
+#define IPC_MESSAGE_START PrerenderMsgStart
+
+// Tells a renderer if it's currently being prerendered.  Must only be set
+// to true before any navigation occurs, and only set to false at most once
+// after that.
+IPC_MESSAGE_ROUTED1(PrerenderMsg_SetIsPrerendering,
+                    bool /* whether the RenderView is prerendering */)
+
+// Specifies that a URL is currently being prerendered.
+IPC_MESSAGE_CONTROL1(PrerenderMsg_AddPrerenderURL,
+                     GURL /* url */)
+
+// Specifies that a URL is no longer being prerendered.
+IPC_MESSAGE_CONTROL1(PrerenderMsg_RemovePrerenderURL,
+                     GURL /* url */)