Move Singleton and related structs to namespace base

ios/chrome/browser/signin/account_consistency_service_factory.mm

 // 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_consistency_service_factory.h"
 
 #include "base/memory/singleton.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "components/signin/ios/browser/account_consistency_service.h"
 #include "ios/chrome/browser/content_settings/cookie_settings_factory.h"
@@ skipping 21 matching lines @@
   if (!experimental_flags::IsWKWebViewEnabled()) {
     return nullptr;
   }
   return static_cast<AccountConsistencyService*>(
       GetInstance()->GetServiceForBrowserState(browser_state, true));
 }
 
 // static
 AccountConsistencyServiceFactory*
 AccountConsistencyServiceFactory::GetInstance() {
-  return Singleton<AccountConsistencyServiceFactory>::get();
+  return base::Singleton<AccountConsistencyServiceFactory>::get();
 }
 
 scoped_ptr<KeyedService>
 AccountConsistencyServiceFactory::BuildServiceInstanceFor(
     web::BrowserState* context) const {
   ios::ChromeBrowserState* chrome_browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
   return make_scoped_ptr(new AccountConsistencyService(
       chrome_browser_state,
       ios::CookieSettingsFactory::GetForBrowserState(chrome_browser_state),
       GaiaCookieManagerServiceFactory::GetForBrowserState(chrome_browser_state),
       ios::SigninManagerFactory::GetForBrowserState(chrome_browser_state)));
 }
 
 }  // namespace ios