Move Singleton and related structs to namespace base

ios/chrome/browser/signin/account_tracker_service_factory.cc

 // Copyright 2015 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 "ios/chrome/browser/signin/account_tracker_service_factory.h"
 
 #include "base/memory/singleton.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "components/signin/core/browser/account_tracker_service.h"
 #include "ios/chrome/browser/signin/signin_client_factory.h"
@@ skipping 12 matching lines @@
 
 // static
 AccountTrackerService* AccountTrackerServiceFactory::GetForBrowserState(
     ios::ChromeBrowserState* browser_state) {
   return static_cast<AccountTrackerService*>(
       GetInstance()->GetServiceForBrowserState(browser_state, true));
 }
 
 // static
 AccountTrackerServiceFactory* AccountTrackerServiceFactory::GetInstance() {
-  return Singleton<AccountTrackerServiceFactory>::get();
+  return base::Singleton<AccountTrackerServiceFactory>::get();
 }
 
 void AccountTrackerServiceFactory::RegisterBrowserStatePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
   AccountTrackerService::RegisterPrefs(registry);
 }
 
 scoped_ptr<KeyedService> AccountTrackerServiceFactory::BuildServiceInstanceFor(
     web::BrowserState* context) const {
   ios::ChromeBrowserState* chrome_browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
   scoped_ptr<AccountTrackerService> service(new AccountTrackerService());
   service->Initialize(
       SigninClientFactory::GetForBrowserState(chrome_browser_state));
   return service.Pass();
 }
 
 }  // namespace ios