Move Singleton and related structs to namespace base

chrome/browser/history/history_service_factory.h

 // Copyright (c) 2012 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_HISTORY_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_HISTORY_HISTORY_SERVICE_FACTORY_H_
 
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 #include "components/keyed_service/core/service_access_type.h"
@@ skipping 19 matching lines @@
 
   static HistoryServiceFactory* GetInstance();
 
   // In the testing profile, we often clear the history before making a new
   // one. This takes care of that work. It should only be used in tests.
   // Note: This does not do any cleanup; it only destroys the service. The
   // calling test is expected to do the cleanup before calling this function.
   static void ShutdownForProfile(Profile* profile);
 
  private:
-  friend struct DefaultSingletonTraits<HistoryServiceFactory>;
+  friend struct base::DefaultSingletonTraits<HistoryServiceFactory>;
 
   HistoryServiceFactory();
   ~HistoryServiceFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
   bool ServiceIsNULLWhileTesting() const override;
 };
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_SERVICE_FACTORY_H_