Move Singleton and related structs to namespace base

chrome/browser/supervised_user/legacy/supervised_user_pref_mapping_service_factory.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 CHROME_BROWSER_SUPERVISED_USER_LEGACY_SUPERVISED_USER_PREF_MAPPING_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_SUPERVISED_USER_LEGACY_SUPERVISED_USER_PREF_MAPPING_SERVICE_FACTORY_H_
 
 #include "base/memory/singleton.h"
 #include "chrome/browser/supervised_user/supervised_users.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 class SupervisedUserPrefMappingService;
 
 class SupervisedUserPrefMappingServiceFactory
     : public BrowserContextKeyedServiceFactory {
  public:
   static SupervisedUserPrefMappingService* GetForBrowserContext(
       content::BrowserContext* profile);
 
   static SupervisedUserPrefMappingServiceFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<SupervisedUserPrefMappingServiceFactory>;
+  friend struct base::DefaultSingletonTraits<
+      SupervisedUserPrefMappingServiceFactory>;
 
   SupervisedUserPrefMappingServiceFactory();
   ~SupervisedUserPrefMappingServiceFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* profile) const override;
 };
 
 #endif  // CHROME_BROWSER_SUPERVISED_USER_LEGACY_SUPERVISED_USER_PREF_MAPPING_SERVICE_FACTORY_H_