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

chrome/browser/prerender/prerender_manager.h

 // Copyright (c) 2011 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 CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_
 #pragma once
 
 #include <list>
 #include <map>
@@ skipping 87 matching lines @@
       FinalStatus final_status);
 
   // For a given TabContents that wants to navigate to the URL supplied,
   // determines whether a preloaded version of the URL can be used,
   // and substitutes the prerendered RVH into the TabContents.  Returns
   // whether or not a prerendered RVH could be used or not.
   bool MaybeUsePreloadedPage(TabContents* tab_contents, const GURL& url);
   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;
 
   // Retrieves the PrerenderContents object for the specified URL, if it
   // has been prerendered.  The caller will then have ownership of the
   // PrerenderContents object and is responsible for freeing it.
   // Returns NULL if the specified URL has not been prerendered.
   PrerenderContents* GetEntry(const GURL& url);
 
@@ skipping 189 matching lines @@
 
   // Cancels pending tasks on deletion.
   ScopedRunnableMethodFactory<PrerenderManager> runnable_method_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderManager);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_