Add OVERRIDE to chrome/browser/.

chrome/browser/prefs/pref_set_observer.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_PREFS_PREF_SET_OBSERVER_H_
 #define CHROME_BROWSER_PREFS_PREF_SET_OBSERVER_H_
 #pragma once
 
 #include <set>
 
@@ skipping 28 matching lines @@
 
   // Create a pref set observer for all preferences relevant to default search.
   static PrefSetObserver* CreateDefaultSearchPrefSetObserver(
       PrefService* pref_service,
       content::NotificationObserver* observer);
 
  private:
   // Overridden from content::NotificationObserver.
   virtual void Observe(int type,
                        const content::NotificationSource& source,
-                       const content::NotificationDetails& details);
+                       const content::NotificationDetails& details) OVERRIDE;
 
   typedef std::set<std::string> PrefSet;
   PrefSet prefs_;
 
   PrefService* pref_service_;
   PrefChangeRegistrar registrar_;
   content::NotificationObserver* observer_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefSetObserver);
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_SET_OBSERVER_H_