Add OVERRIDE to chrome/browser/.

chrome/browser/history/in_memory_history_backend.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.
 
 // Contains the history backend wrapper around the in-memory URL database. This
 // object maintains an in-memory cache of the subset of history required to do
 // in-line autocomplete.
 //
 // It is created on the history thread and passed to the main thread where
 // operations can be completed synchronously. It listens for notifications
@@ skipping 49 matching lines @@
   // Returns the underlying database associated with this backend. The current
   // autocomplete code was written fro this, but it should probably be removed
   // so that it can deal directly with this object, rather than the DB.
   InMemoryDatabase* db() const {
     return db_.get();
   }
 
   // Notification callback.
   virtual void Observe(int type,
                        const content::NotificationSource& source,
-                       const content::NotificationDetails& details);
+                       const content::NotificationDetails& details) OVERRIDE;
 
   // Return the quick history index.
   history::InMemoryURLIndex* InMemoryIndex() const { return index_.get(); }
 
  private:
   FRIEND_TEST_ALL_PREFIXES(HistoryBackendTest, DeleteAll);
 
   // Handler for NOTIFY_HISTORY_TYPED_URLS_MODIFIED.
   void OnTypedURLsModified(const URLsModifiedDetails& details);
 
@@ skipping 16 matching lines @@
 
   // The index used for quick history lookups.
   scoped_ptr<history::InMemoryURLIndex> index_;
 
   DISALLOW_COPY_AND_ASSIGN(InMemoryHistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_IN_MEMORY_HISTORY_BACKEND_H_