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

chrome/browser/gtk/browser_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_TOOLBAR_GTK_H_
 #define CHROME_BROWSER_GTK_BROWSER_TOOLBAR_GTK_H_
 #pragma once
 
 #include <gtk/gtk.h>
 #include <string>
@@ skipping 80 matching lines @@
   // Overridden from MenuGtk::Delegate:
   virtual void StoppedShowing();
   virtual GtkIconSet* GetIconSetForId(int idr);
   virtual bool AlwaysShowIconForCmd(int command_id) const;
 
   // Overridden from menus::AcceleratorProvider:
   virtual bool GetAcceleratorForCommandId(int id,
                                           menus::Accelerator* accelerator);
 
   // NotificationObserver implementation.
-  void Observe(NotificationType type,
-               const NotificationSource& source,
-               const NotificationDetails& details);
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
 
   Profile* profile() { return profile_; }
   void SetProfile(Profile* profile);
 
   // Message that we should react to a state change.
   void UpdateTabContents(TabContents* contents, bool should_restore_state);
 
  private:
   // Connect/Disconnect signals for dragging a url onto the home button.
   void SetUpDragForHomeButton(bool enable);
@@ skipping 96 matching lines @@
   // rendering.
   OwnedWidgetGtk offscreen_entry_;
 
   // Manages the home button drop signal handler.
   scoped_ptr<GtkSignalRegistrar> drop_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserToolbarGtk);
 };
 
 #endif  // CHROME_BROWSER_GTK_BROWSER_TOOLBAR_GTK_H_