Keep a copy of page id in RenderViewHost.

content/browser/renderer_host/render_view_host_impl.h

Index: content/browser/renderer_host/render_view_host_impl.h
diff --git a/content/browser/renderer_host/render_view_host_impl.h b/content/browser/renderer_host/render_view_host_impl.h
index e2a97648b6317adaadf1d23a78f26b0530f14a46..b099a7b280f63bef518c334f79777250201be3dc 100644
--- a/content/browser/renderer_host/render_view_host_impl.h
+++ b/content/browser/renderer_host/render_view_host_impl.h
@@ -547,6 +547,11 @@ class CONTENT_EXPORT RenderViewHostImpl
   // TODO(nasko): Move to RenderFrameHost, as this is per-frame state.
   scoped_ptr<FrameMsg_Navigate_Params> suspended_nav_params_;
 
+  // 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_;