Update {virtual,override,final} to follow C++11 style.

chrome/browser/ui/android/context_menu_helper.h

 // Copyright 2013 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_UI_ANDROID_CONTEXT_MENU_HELPER_H_
 #define CHROME_BROWSER_UI_ANDROID_CONTEXT_MENU_HELPER_H_
 
 #include "base/android/jni_android.h"
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "content/public/browser/web_contents_user_data.h"
 #include "content/public/common/context_menu_params.h"
 
 namespace content {
 struct ContextMenuParams;
 class WebContents;
 }
 
 class ContextMenuHelper
     : public content::WebContentsUserData<ContextMenuHelper> {
  public:
-  virtual ~ContextMenuHelper();
+  ~ContextMenuHelper() override;
 
   void ShowContextMenu(const content::ContextMenuParams& params);
 
   void ShowCustomContextMenu(
       const content::ContextMenuParams& params,
       const base::Callback<void(int)>& callback);
 
   void SetPopulator(jobject jpopulator);
 
   // Methods called from Java via JNI ------------------------------------------
@@ skipping 13 matching lines @@
 
   base::Callback<void(int)> context_menu_callback_;
   content::ContextMenuParams context_menu_params_;
 
   DISALLOW_COPY_AND_ASSIGN(ContextMenuHelper);
 };
 
 bool RegisterContextMenuHelper(JNIEnv* env);
 
 #endif  // CHROME_BROWSER_UI_ANDROID_CONTEXT_MENU_HELPER_H_