Prevent a possible crash on omnibox navigation.

chrome/browser/ui/omnibox/omnibox_navigation_observer.h

 // Copyright 2012 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_UI_OMNIBOX_OMNIBOX_NAVIGATION_OBSERVER_H_
 #define CHROME_BROWSER_UI_OMNIBOX_OMNIBOX_NAVIGATION_OBSERVER_H_
 
 #include <string>
 
 #include "base/memory/ref_counted.h"
@@ skipping 63 matching lines @@
 
   // content::NotificationObserver:
   void Observe(int type,
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
   // content::WebContentsObserver:
   void DidStartNavigationToPendingEntry(
       const GURL& url,
       content::NavigationController::ReloadType reload_type) override;
+  void DidFailProvisionalLoad(content::RenderFrameHost* render_frame_host,
+                              const GURL& validated_url,
+                              int error_code,
+                              const base::string16& error_description) override;
   void NavigationEntryCommitted(
       const content::LoadCommittedDetails& load_details) override;
   void WebContentsDestroyed() override;
 
   // net::URLFetcherDelegate:
   void OnURLFetchComplete(const net::URLFetcher* source) override;
 
   // Once the load has committed and any URL fetch has completed, this displays
   // the alternate nav infobar if necessary, and deletes |this|.
   void OnAllLoadingFinished();
 
   const base::string16 text_;
   const AutocompleteMatch match_;
   const AutocompleteMatch alternate_nav_match_;
   scoped_refptr<ShortcutsBackend> shortcuts_backend_;  // NULL in incognito.
   scoped_ptr<net::URLFetcher> fetcher_;
   LoadState load_state_;
   FetchState fetch_state_;
 
   content::NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(OmniboxNavigationObserver);
 };
 
 #endif  // CHROME_BROWSER_UI_OMNIBOX_OMNIBOX_NAVIGATION_OBSERVER_H_