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

extensions/browser/mock_extension_system.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_MOCK_EXTENSION_SYSTEM_H_
 #define EXTENSIONS_BROWSER_MOCK_EXTENSION_SYSTEM_H_
 
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "extensions/browser/extension_registry_factory.h"
 #include "extensions/browser/extension_system.h"
@@ skipping 53 matching lines @@
 template <typename T>
 class MockExtensionSystemFactory : public ExtensionSystemProvider {
  public:
   MockExtensionSystemFactory()
       : ExtensionSystemProvider(
             "MockExtensionSystem",
             BrowserContextDependencyManager::GetInstance()) {
     DependsOn(ExtensionRegistryFactory::GetInstance());
   }
 
-  virtual ~MockExtensionSystemFactory() {}
+  ~MockExtensionSystemFactory() override {}
 
   // BrowserContextKeyedServiceFactory overrides:
-  virtual KeyedService* BuildServiceInstanceFor(
+  KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override {
     return new T(context);
   }
 
   // ExtensionSystemProvider overrides:
-  virtual ExtensionSystem* GetForBrowserContext(
+  ExtensionSystem* GetForBrowserContext(
       content::BrowserContext* context) override {
     return static_cast<ExtensionSystem*>(
         GetServiceForBrowserContext(context, true));
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MockExtensionSystemFactory);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_MOCK_EXTENSION_SYSTEM_H_