Keep a copy of page id in RenderViewHost.

content/browser/renderer_host/render_view_host_impl.h

 // 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.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_VIEW_HOST_IMPL_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_VIEW_HOST_IMPL_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 448 matching lines @@
   scoped_refptr<SiteInstanceImpl> instance_;
 
   // true if we are currently waiting for a response for drag context
   // information.
   bool waiting_for_drag_context_response_;
 
   // A bitwise OR of bindings types that have been enabled for this RenderView.
   // See BindingsPolicy for details.
   int enabled_bindings_;
 
+  // The most recent page ID we've heard from the renderer process.  This is
+  // used as context when other session history related IPCs arrive.
+  // TODO(creis): Allocate this in WebContents/NavigationController instead.
+  int32 page_id_;
 
   // The current state of this RVH.
   // TODO(nasko): Move to RenderFrameHost, as this is per-frame state.
   RenderViewHostImplState rvh_state_;
 
   // Routing ID for the main frame's RenderFrameHost.
   int main_frame_routing_id_;
 
   // If we were asked to RunModal, then this will hold the reply_msg that we
   // must return to the renderer to unblock it.
@@ skipping 58 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(RenderViewHostImpl);
 };
 
 #if defined(COMPILER_MSVC)
 #pragma warning(pop)
 #endif
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_VIEW_HOST_IMPL_H_