Fix issues when PrerenderContents::Destroy() is called during TabContents destruction.

chrome/browser/prerender/prerender_manager.h

Index: chrome/browser/prerender/prerender_manager.h
===================================================================
--- chrome/browser/prerender/prerender_manager.h	(revision 85626)
+++ chrome/browser/prerender/prerender_manager.h	(working copy)
@@ -105,8 +105,10 @@
   bool MaybeUsePreloadedPageOld(TabContents* tab_contents, const GURL& url);
 
   // Moves a PrerenderContents to the pending delete list from the list of
-  // active prerenders when prerendering should be cancelled.
-  void MoveEntryToPendingDelete(PrerenderContents* entry);
+  // active prerenders when prerendering should be cancelled.  Returns true
+  // on success.  If |entry| was not an active prerender, returns false and
+  // does not move |entry| to the pending delete list.
+  bool MoveEntryToPendingDelete(PrerenderContents* entry);
 
   // Checks if the PrerenderContents has been added to the pending delete list.
   bool IsPendingDelete(PrerenderContents* entry) const;