Standardize usage of virtual/override/final in extensions/

extensions/common/manifest_handlers/offline_enabled_info.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 EXTENSIONS_COMMON_MANIFEST_HANDLERS_OFFLINE_ENABLED_INFO_H_
 #define EXTENSIONS_COMMON_MANIFEST_HANDLERS_OFFLINE_ENABLED_INFO_H_
 
 #include <string>
 #include <vector>
 
 #include "extensions/common/extension.h"
 #include "extensions/common/manifest.h"
 #include "extensions/common/manifest_handler.h"
 
 namespace extensions {
 
 struct OfflineEnabledInfo : public Extension::ManifestData {
   explicit OfflineEnabledInfo(bool offline_enabled);
-  virtual ~OfflineEnabledInfo();
+  ~OfflineEnabledInfo() override;
 
   // Whether the extension or app should be enabled when offline.
   // Defaults to false, except for platform apps which are offline by default.
   bool offline_enabled;
 
   static bool IsOfflineEnabled(const Extension* extension);
 };
 
 // Parses the "offline_enabled" manifest key.
 class OfflineEnabledHandler : public ManifestHandler {
  public:
   OfflineEnabledHandler();
-  virtual ~OfflineEnabledHandler();
+  ~OfflineEnabledHandler() override;
 
-  virtual bool Parse(Extension* extension, base::string16* error) override;
-  virtual bool AlwaysParseForType(Manifest::Type type) const override;
+  bool Parse(Extension* extension, base::string16* error) override;
+  bool AlwaysParseForType(Manifest::Type type) const override;
 
  private:
-  virtual const std::vector<std::string> Keys() const override;
+  const std::vector<std::string> Keys() const override;
 
   DISALLOW_COPY_AND_ASSIGN(OfflineEnabledHandler);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_MANIFEST_HANDLERS_OFFLINE_ENABLED_INFO_H_