Move Singleton and related structs to namespace base

chrome/browser/history/web_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_WEB_HISTORY_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_HISTORY_WEB_HISTORY_SERVICE_FACTORY_H_
 
 #include "base/memory/singleton.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
@@ skipping 11 matching lines @@
 
   // Get the WebHistoryService for |profile|, creating one if needed.
   static history::WebHistoryService* GetForProfile(Profile* profile);
 
  protected:
   // Overridden from BrowserContextKeyedServiceFactory.
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
 
  private:
-  friend struct DefaultSingletonTraits<WebHistoryServiceFactory>;
+  friend struct base::DefaultSingletonTraits<WebHistoryServiceFactory>;
 
   WebHistoryServiceFactory();
   ~WebHistoryServiceFactory() override;
 
   DISALLOW_COPY_AND_ASSIGN(WebHistoryServiceFactory);
 };
 
 #endif  // CHROME_BROWSER_HISTORY_WEB_HISTORY_SERVICE_FACTORY_H_