Standardize usage of virtual/override/final in extensions/

extensions/common/manifest_handlers/nacl_modules_handler.h

 // Copyright 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_COMMON_MANIFEST_HANDLERS_NACL_MODULES_HANDLER_H_
 #define EXTENSIONS_COMMON_MANIFEST_HANDLERS_NACL_MODULES_HANDLER_H_
 
 #include <list>
 #include <string>
 
@@ skipping 10 matching lines @@
       const Extension* extension);
 
   GURL url;
   std::string mime_type;
 };
 
 // Parses the "nacl_modules" manifest key.
 class NaClModulesHandler : public ManifestHandler {
  public:
   NaClModulesHandler();
-  virtual ~NaClModulesHandler();
+  ~NaClModulesHandler() override;
 
-  virtual bool Parse(Extension* extension, base::string16* error) override;
+  bool Parse(Extension* extension, base::string16* error) override;
 
  private:
-  virtual const std::vector<std::string> Keys() const override;
+  const std::vector<std::string> Keys() const override;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_MANIFEST_HANDLERS_NACL_MODULES_HANDLER_H_