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

chrome/browser/dom_ui/foreign_session_handler.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_FOREIGN_SESSION_HANDLER_H_
 #define CHROME_BROWSER_DOM_UI_FOREIGN_SESSION_HANDLER_H_
 #pragma once
 
 #include <vector>
 
@@ skipping 12 matching lines @@
   virtual void RegisterMessages();
 
   ForeignSessionHandler();
   virtual ~ForeignSessionHandler() {}
 
  private:
   // Used to register ForeignSessionHandler for notifications.
   void Init();
 
   // Determines how ForeignSessionHandler will interact with the new tab page.
-  void Observe(NotificationType type, const NotificationSource& source,
-               const NotificationDetails& details);
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
 
   // Returns a pointer to the current session model associator or NULL.
   SessionModelAssociator* GetModelAssociator();
 
   // Determines whether foreign sessions should be obtained from the sync model.
   // This is a javascript callback handler, and it is also called when the sync
   // model has changed and the new tab page needs to reflect the changes.
   void HandleGetForeignSessions(const ListValue* args);
 
   // Helper for reopening a foreign session in a new browser window.
   void OpenForeignSession(SessionModelAssociator* associator, int64 id);
 
   // Helper for listing the foreign sessions on the new tab page.
   void GetForeignSessions(SessionModelAssociator* associator);
 
   // Determines which session is to be opened, and then calls
   // OpenForeignSession, to begin the process of opening a new browser window.
   // This is a javascript callback handler.
   void HandleReopenForeignSession(const ListValue* args);
 
   // The Registrar used to register ForeignSessionHandler for notifications.
   NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(ForeignSessionHandler);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_DOM_UI_FOREIGN_SESSION_HANDLER_H_