Move Singleton and related structs to namespace base

chrome/browser/history/top_sites_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_HISTORY_TOP_SITES_FACTORY_H_
 #define CHROME_BROWSER_HISTORY_TOP_SITES_FACTORY_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
 #include "components/keyed_service/content/refcounted_browser_context_keyed_service_factory.h"
 
 class Profile;
 
+namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
+}
 
 namespace history {
 struct PrepopulatedPage;
 class TopSites;
 }
 
 class Profile;
 
 // Used for creating and fetching a per-profile instance of the
 // TopSites.
 class TopSitesFactory : public RefcountedBrowserContextKeyedServiceFactory {
  public:
   // Get the TopSites service for |profile|, creating one if needed.
   static scoped_refptr<history::TopSites> GetForProfile(Profile* profile);
 
   // Get the singleton instance of the factory.
   static TopSitesFactory* GetInstance();
 
   // Creates a TopSites service for |context| with |prepopulated_page_list|.
   // Public for testing.
   static scoped_refptr<history::TopSites> BuildTopSites(
       content::BrowserContext* context,
       const std::vector<history::PrepopulatedPage>& prepopulated_page_list);
 
  private:
-  friend struct DefaultSingletonTraits<TopSitesFactory>;
+  friend struct base::DefaultSingletonTraits<TopSitesFactory>;
 
   TopSitesFactory();
   ~TopSitesFactory() override;
 
   // Overridden from BrowserContextKeyedServiceFactory.
   scoped_refptr<RefcountedKeyedService> BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
   void RegisterProfilePrefs(
       user_prefs::PrefRegistrySyncable* registry) override;
   bool ServiceIsNULLWhileTesting() const override;
 
   DISALLOW_COPY_AND_ASSIGN(TopSitesFactory);
 };
 
 #endif  // CHROME_BROWSER_HISTORY_TOP_SITES_FACTORY_H_