Move Singleton and related structs to namespace base

ios/chrome/browser/dom_distiller/dom_distiller_service_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 IOS_CHROME_BROWSER_DOM_DISTILLER_DOM_DISTILLER_SERVICE_FACTORY_H_
 #define IOS_CHROME_BROWSER_DOM_DISTILLER_DOM_DISTILLER_SERVICE_FACTORY_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "components/keyed_service/ios/browser_state_keyed_service_factory.h"
 
 template <typename T>
-struct DefaultSingletonTraits;
+struct base::DefaultSingletonTraits;
 
 namespace dom_distiller {
 class DomDistillerService;
 }
 
 namespace ios {
 class ChromeBrowserState;
 }
 
 namespace dom_distiller {
 
 class DomDistillerServiceFactory : public BrowserStateKeyedServiceFactory {
  public:
   static DomDistillerServiceFactory* GetInstance();
   static DomDistillerService* GetForBrowserState(
       ios::ChromeBrowserState* browser_state);
 
  private:
-  friend struct DefaultSingletonTraits<DomDistillerServiceFactory>;
+  friend struct base::DefaultSingletonTraits<DomDistillerServiceFactory>;
 
   DomDistillerServiceFactory();
   ~DomDistillerServiceFactory() override;
 
   // BrowserStateKeyedServiceFactory implementation.
   scoped_ptr<KeyedService> BuildServiceInstanceFor(
       web::BrowserState* context) const override;
   web::BrowserState* GetBrowserStateToUse(
       web::BrowserState* context) const override;
 
   DISALLOW_COPY(DomDistillerServiceFactory);
 };
 
 }  // namespace dom_distiller
 
 #endif  // IOS_CHROME_BROWSER_DOM_DISTILLER_DOM_DISTILLER_SERVICE_FACTORY_H_