Safely cancel prerenders on threads other than the UI thread

chrome/browser/prerender/prerender_contents.h

Index: chrome/browser/prerender/prerender_contents.h
===================================================================
--- chrome/browser/prerender/prerender_contents.h	(revision 85771)
+++ chrome/browser/prerender/prerender_contents.h	(working copy)
@@ -317,6 +317,8 @@
 
   bool has_stopped_loading_;
 
+  // This must be the same value as the PrerenderTracker has recorded for
+  // |this|, when |this| has a RenderView.
   FinalStatus final_status_;
 
   bool prerendering_has_started_;
@@ -335,6 +337,10 @@
 
   scoped_ptr<PrerenderRenderViewHostObserver> render_view_host_observer_;
 
+  // These are -1 before a RenderView is created.
+  int child_id_;
+  int route_id_;
+
   DISALLOW_COPY_AND_ASSIGN(PrerenderContents);
 };