Move Singleton and related structs to namespace base

chrome/browser/background/background_contents_service_factory.h

 // Copyright (c) 2011 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_BACKGROUND_BACKGROUND_CONTENTS_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_BACKGROUND_BACKGROUND_CONTENTS_SERVICE_FACTORY_H_
 
 #include "base/compiler_specific.h"
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 class BackgroundContentsService;
 class Profile;
 
 // Singleton that owns all BackgroundContentsServices and associates them with
 // Profiles. Listens for the Profile's destruction notification and cleans up
 // the associated BackgroundContentsService.
 class BackgroundContentsServiceFactory
     : public BrowserContextKeyedServiceFactory {
  public:
   static BackgroundContentsService* GetForProfile(Profile* profile);
 
   static BackgroundContentsServiceFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<BackgroundContentsServiceFactory>;
+  friend struct base::DefaultSingletonTraits<BackgroundContentsServiceFactory>;
 
   BackgroundContentsServiceFactory();
   ~BackgroundContentsServiceFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* profile) const override;
   void RegisterProfilePrefs(
       user_prefs::PrefRegistrySyncable* registry) override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
   bool ServiceIsCreatedWithBrowserContext() const override;
   bool ServiceIsNULLWhileTesting() const override;
 };
 
 #endif  // CHROME_BROWSER_BACKGROUND_BACKGROUND_CONTENTS_SERVICE_FACTORY_H_