Move Singleton and related structs to namespace base

extensions/shell/browser/shell_extension_system_factory.cc

 // 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.
 
 #include "extensions/shell/browser/shell_extension_system_factory.h"
 
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "extensions/browser/extension_prefs_factory.h"
 #include "extensions/browser/extension_registry_factory.h"
 #include "extensions/shell/browser/shell_extension_system.h"
 
 using content::BrowserContext;
 
 namespace extensions {
 
 ExtensionSystem* ShellExtensionSystemFactory::GetForBrowserContext(
     BrowserContext* context) {
   return static_cast<ShellExtensionSystem*>(
       GetInstance()->GetServiceForBrowserContext(context, true));
 }
 
 // static
 ShellExtensionSystemFactory* ShellExtensionSystemFactory::GetInstance() {
-  return Singleton<ShellExtensionSystemFactory>::get();
+  return base::Singleton<ShellExtensionSystemFactory>::get();
 }
 
 ShellExtensionSystemFactory::ShellExtensionSystemFactory()
     : ExtensionSystemProvider("ShellExtensionSystem",
                               BrowserContextDependencyManager::GetInstance()) {
   DependsOn(ExtensionPrefsFactory::GetInstance());
   DependsOn(ExtensionRegistryFactory::GetInstance());
 }
 
 ShellExtensionSystemFactory::~ShellExtensionSystemFactory() {
 }
 
 KeyedService* ShellExtensionSystemFactory::BuildServiceInstanceFor(
     BrowserContext* context) const {
   return new ShellExtensionSystem(context);
 }
 
 BrowserContext* ShellExtensionSystemFactory::GetBrowserContextToUse(
     BrowserContext* context) const {
   // Use a separate instance for incognito.
   return context;
 }
 
 bool ShellExtensionSystemFactory::ServiceIsCreatedWithBrowserContext() const {
   return true;
 }
 
 }  // namespace extensions