Standardize usage of virtual/override/final in extensions/

extensions/browser/updater/null_extension_cache.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_BROWSER_UPDATER_NULL_EXTENSION_CACHE_H_
 #define EXTENSIONS_BROWSER_UPDATER_NULL_EXTENSION_CACHE_H_
 
 #include "extensions/browser/updater/extension_cache.h"
 
 namespace extensions {
 
 // Implements a pass-thru (i.e. do-nothing) ExtensionCache.
 class NullExtensionCache : public ExtensionCache {
  public:
   NullExtensionCache();
-  virtual ~NullExtensionCache();
+  ~NullExtensionCache() override;
 
   // ExtensionCache implementation.
-  virtual void Start(const base::Closure& callback) override;
-  virtual void Shutdown(const base::Closure& callback) override;
-  virtual void AllowCaching(const std::string& id) override;
-  virtual bool GetExtension(const std::string& id,
-                            base::FilePath* file_path,
-                            std::string* version) override;
-  virtual void PutExtension(const std::string& id,
-                            const base::FilePath& file_path,
-                            const std::string& version,
-                            const PutExtensionCallback& callback) override;
+  void Start(const base::Closure& callback) override;
+  void Shutdown(const base::Closure& callback) override;
+  void AllowCaching(const std::string& id) override;
+  bool GetExtension(const std::string& id,
+                    base::FilePath* file_path,
+                    std::string* version) override;
+  void PutExtension(const std::string& id,
+                    const base::FilePath& file_path,
+                    const std::string& version,
+                    const PutExtensionCallback& callback) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NullExtensionCache);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_UPDATER_NULL_EXTENSION_CACHE_H_