Standardize usage of virtual/override/final in extensions/

extensions/browser/api/declarative_content/content_rules_registry.h

 // Copyright (c) 2014 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 EXTENSIONS_BROWSER_API_DECLARATIVE_CONTENT_CONTENT_RULES_REGISTRY_H__
 #define EXTENSIONS_BROWSER_API_DECLARATIVE_CONTENT_CONTENT_RULES_REGISTRY_H__
 
 #include <string>
 
 #include "content/public/browser/browser_thread.h"
@@ skipping 31 matching lines @@
       content::WebContents* contents,
       const std::vector<std::string>& matching_css_selectors) = 0;
 
   // Applies all content rules given that a tab was just navigated.
   virtual void DidNavigateMainFrame(
       content::WebContents* tab,
       const content::LoadCommittedDetails& details,
       const content::FrameNavigateParams& params) = 0;
 
  protected:
-  virtual ~ContentRulesRegistry() {}
+  ~ContentRulesRegistry() override {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ContentRulesRegistry);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_API_DECLARATIVE_CONTENT_CONTENT_RULES_REGISTRY_H__