Move Singleton and related structs to namespace base

chrome/browser/extensions/extension_sync_service_factory.h

 // Copyright 2013 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_EXTENSIONS_EXTENSION_SYNC_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_SYNC_SERVICE_FACTORY_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 class ExtensionSyncService;
 
 class ExtensionSyncServiceFactory : public BrowserContextKeyedServiceFactory {
  public:
   static ExtensionSyncService* GetForBrowserContext(
       content::BrowserContext* context);
 
   static ExtensionSyncServiceFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<ExtensionSyncServiceFactory>;
+  friend struct base::DefaultSingletonTraits<ExtensionSyncServiceFactory>;
 
   ExtensionSyncServiceFactory();
   ~ExtensionSyncServiceFactory() override;
 
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SYNC_SERVICE_FACTORY_H_