Move Singleton and related structs to namespace base

chrome/browser/push_messaging/push_messaging_service_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_PUSH_MESSAGING_PUSH_MESSAGING_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_PUSH_MESSAGING_PUSH_MESSAGING_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 PushMessagingServiceImpl;
 
 class PushMessagingServiceFactory : public BrowserContextKeyedServiceFactory {
  public:
   static PushMessagingServiceImpl* GetForProfile(
       content::BrowserContext* profile);
   static PushMessagingServiceFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<PushMessagingServiceFactory>;
+  friend struct base::DefaultSingletonTraits<PushMessagingServiceFactory>;
 
   PushMessagingServiceFactory();
   ~PushMessagingServiceFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* profile) const override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
 
   DISALLOW_COPY_AND_ASSIGN(PushMessagingServiceFactory);
 };
 
 #endif  // CHROME_BROWSER_PUSH_MESSAGING_PUSH_MESSAGING_SERVICE_FACTORY_H_