Move Singleton and related structs to namespace base

chrome/browser/signin/cross_device_promo_factory.h

 // 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.
 
 #ifndef CHROME_BROWSER_SIGNIN_CROSS_DEVICE_PROMO_FACTORY_H_
 #define CHROME_BROWSER_SIGNIN_CROSS_DEVICE_PROMO_FACTORY_H_
 
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 class CrossDevicePromo;
 class Profile;
 
 // Singleton that owns all CrossDevicePromos and associates them with
 // Profiles.
 class CrossDevicePromoFactory : public BrowserContextKeyedServiceFactory {
  public:
   // Returns the instance of CrossDevicePromo associated with this profile,
   // creating one if none exists.
   static CrossDevicePromo* GetForProfile(Profile* profile);
 
   // Returns an instance of the CrossDevicePromoFactory singleton.
   static CrossDevicePromoFactory* GetInstance();
 
   // Implementation of BrowserContextKeyedServiceFactory.
   void RegisterProfilePrefs(
       user_prefs::PrefRegistrySyncable* registry) override;
 
  private:
-  friend struct DefaultSingletonTraits<CrossDevicePromoFactory>;
+  friend struct base::DefaultSingletonTraits<CrossDevicePromoFactory>;
 
   CrossDevicePromoFactory();
   ~CrossDevicePromoFactory() override;
 
   // BrowserContextKeyedServiceFactory
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
 
   DISALLOW_COPY_AND_ASSIGN(CrossDevicePromoFactory);
 };
 
 #endif  // CHROME_BROWSER_SIGNIN_CROSS_DEVICE_PROMO_FACTORY_H_