Ensure that PageID's of prerendered pages do not exceed the Page ID of the

chrome/browser/prerender/prerender_contents.h

Index: chrome/browser/prerender/prerender_contents.h
===================================================================
--- chrome/browser/prerender/prerender_contents.h	(revision 86289)
+++ chrome/browser/prerender/prerender_contents.h	(working copy)
@@ -254,6 +254,8 @@
   // new tab.
   void CommitHistory(TabContents* tc);
 
+  int32 starting_page_id() { return starting_page_id_; }
+
  protected:
   PrerenderContents(PrerenderManager* prerender_manager,
                     Profile* profile,
@@ -357,6 +359,9 @@
   int child_id_;
   int route_id_;
 
+  // Page ID at which prerendering started.
+  int32 starting_page_id_;
+
   DISALLOW_COPY_AND_ASSIGN(PrerenderContents);
 };