Speculative fix for crash. Crashes seem to indicate

chrome/browser/extensions/extension_webnavigation_api.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.
 
 // Defines the Chrome Extensions WebNavigation API functions for observing and
 // intercepting navigation events, as specified in
 // chrome/common/extensions/api/extension_api.json.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_EXTENSION_WEBNAVIGATION_API_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_WEBNAVIGATION_API_H_
@@ skipping 180 matching lines @@
 
   // Handler for the NOTIFICATION_RETARGETING event. The method takes the
   // details of such an event and stores them for the later
   // NOTIFICATION_TAB_ADDED event.
   void Retargeting(const content::RetargetingDetails* details);
 
   // Handler for the NOTIFICATION_TAB_ADDED event. The method takes the details
   // of such an event and creates a JSON formated extension event from it.
   void TabAdded(TabContents* tab_contents);
 
+  // Handler for NOTIFICATION_TAB_CONTENTS_DESTROYED. If |tab_contents| is
+  // in |pending_tab_contents_|, it is removed.
+  void TabDestroyed(TabContents* tab_contents);
+
   // Mapping pointers to TabContents objects to information about how they got
   // created.
   std::map<TabContents*, PendingTabContents> pending_tab_contents_;
 
   // Used for tracking registrations to navigation notifications.
   NotificationRegistrar registrar_;
 
   // The profile that owns us via ExtensionService.
   Profile* profile_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionWebNavigationEventRouter);
 };
 
 // API function that returns the state of a given frame.
 class GetFrameFunction : public SyncExtensionFunction {
   virtual ~GetFrameFunction() {}
   virtual bool RunImpl();
   DECLARE_EXTENSION_FUNCTION_NAME("experimental.webNavigation.getFrame")
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_WEBNAVIGATION_API_H_