Add the "virtual" keyword on method overrides that are missing it.

chrome/browser/dom_ui/new_tab_ui.h

 // Copyright (c) 2010 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_DOM_UI_NEW_TAB_UI_H_
 #define CHROME_BROWSER_DOM_UI_NEW_TAB_UI_H_
 #pragma once
 
 #include <string>
 
@@ skipping 71 matching lines @@
 
     // Pointer back to the original profile.
     Profile* profile_;
 
     DISALLOW_COPY_AND_ASSIGN(NewTabHTMLSource);
   };
 
  private:
   FRIEND_TEST_ALL_PREFIXES(NewTabUITest, UpdateUserPrefsVersion);
 
-  void Observe(NotificationType type,
-               const NotificationSource& source,
-               const NotificationDetails& details);
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
 
   // Reset the CSS caches.
   void InitializeCSSCaches();
 
   // Updates the user prefs version and calls |MigrateUserPrefs| if needed.
   // Returns true if the version was updated.
   static bool UpdateUserPrefsVersion(PrefService* prefs);
 
   NotificationRegistrar registrar_;
 
   // The preference version. This used for migrating prefs of the NTP.
   static const int current_pref_version_ = 3;
 
   DISALLOW_COPY_AND_ASSIGN(NewTabUI);
 };
 
 #endif  // CHROME_BROWSER_DOM_UI_NEW_TAB_UI_H_