chromeos: Add "virtual" to d'tor to appease clang.

chrome/browser/chromeos/legacy_window_manager/initial_browser_window_observer.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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_LEGACY_WINDOW_MANAGER_INITIAL_BROWSER_WINDOW_OBSERVER_H_
 #define CHROME_BROWSER_CHROMEOS_LEGACY_WINDOW_MANAGER_INITIAL_BROWSER_WINDOW_OBSERVER_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ skipping 11 matching lines @@
 // when it sees the first Chrome browser window get mapped post-login.  Tests
 // then watch for this file to determine when login is completed.  There's no X
 // window manager running for Aura builds, so we make Chrome replicate this
 // behavior itself.
 //
 // TODO(derat): Once Aura is fully in use in Chrome OS, remove this and make
 // tests instead use pyauto to communicate with Chrome.
 class InitialBrowserWindowObserver : public content::NotificationObserver {
  public:
   InitialBrowserWindowObserver();
-  ~InitialBrowserWindowObserver() {}
+  virtual ~InitialBrowserWindowObserver() {}
 
   // content::NotificationObserver implementation:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
  private:
   content::NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(InitialBrowserWindowObserver);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LEGACY_WINDOW_MANAGER_INITIAL_BROWSER_WINDOW_OBSERVER_H_