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

chrome/browser/gtk/browser_actions_toolbar_gtk.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_GTK_BROWSER_ACTIONS_TOOLBAR_GTK_H_
 #define CHROME_BROWSER_GTK_BROWSER_ACTIONS_TOOLBAR_GTK_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 43 matching lines @@
 
   Browser* browser() { return browser_; }
 
   // Returns the currently selected tab ID, or -1 if there is none.
   int GetCurrentTabId();
 
   // Update the display of all buttons.
   void Update();
 
   // NotificationObserver implementation.
-  void Observe(NotificationType type,
-               const NotificationSource& source,
-               const NotificationDetails& details);
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
 
   bool animating() {
     return resize_animation_.is_animating();
   }
 
  private:
   friend class BrowserActionButton;
 
   // Initialize drag and drop.
   void SetupDrags();
@@ skipping 139 matching lines @@
   GtkSignalRegistrar signals_;
 
   NotificationRegistrar registrar_;
 
   ScopedRunnableMethodFactory<BrowserActionsToolbarGtk> method_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserActionsToolbarGtk);
 };
 
 #endif  // CHROME_BROWSER_GTK_BROWSER_ACTIONS_TOOLBAR_GTK_H_