Move Singleton and related structs to namespace base

ios/web/webui/web_ui_ios_controller_factory_registry.h

 // Copyright 2014 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 IOS_WEB_WEBUI_WEB_UI_IOS_CONTROLLER_FACTORY_REGISTRY_H_
 #define IOS_WEB_WEBUI_WEB_UI_IOS_CONTROLLER_FACTORY_REGISTRY_H_
 
 #include "base/memory/singleton.h"
 #include "ios/public/provider/web/web_ui_ios_controller_factory.h"
 
 namespace web {
 
 // A singleton which holds on to all the registered WebUIIOSControllerFactory
 // instances.
 class WebUIIOSControllerFactoryRegistry : public WebUIIOSControllerFactory {
  public:
   static WebUIIOSControllerFactoryRegistry* GetInstance();
 
   // WebUIIOSControllerFactory implementation. Each method loops through the
   // same method on all the factories.
   WebUIIOSController* CreateWebUIIOSControllerForURL(
       WebUIIOS* web_ui,
       const GURL& url) const override;
 
  private:
-  friend struct DefaultSingletonTraits<WebUIIOSControllerFactoryRegistry>;
+  friend struct base::DefaultSingletonTraits<WebUIIOSControllerFactoryRegistry>;
 
   WebUIIOSControllerFactoryRegistry();
   ~WebUIIOSControllerFactoryRegistry() override;
 
   DISALLOW_COPY_AND_ASSIGN(WebUIIOSControllerFactoryRegistry);
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_WEBUI_WEB_UI_IOS_CONTROLLER_FACTORY_REGISTRY_H_