Move Singleton and related structs to namespace base

ios/chrome/browser/enhanced_bookmarks/enhanced_bookmark_model_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_ENHANCED_BOOKMARKS_ENHANCED_BOOKMARK_MODEL_FACTORY_H_
 #define IOS_CHROME_BROWSER_ENHANCED_BOOKMARKS_ENHANCED_BOOKMARK_MODEL_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 ios {
 class ChromeBrowserState;
 }
 
 namespace enhanced_bookmarks {
 
 class EnhancedBookmarkModel;
 
 // A factory to create BookmarkServerClusterService and associate them to
 // ios::ChromeBrowserState.
 class EnhancedBookmarkModelFactory : public BrowserStateKeyedServiceFactory {
  public:
   static EnhancedBookmarkModelFactory* GetInstance();
   static EnhancedBookmarkModel* GetForBrowserState(
       ios::ChromeBrowserState* browser_state);
 
  private:
-  friend struct DefaultSingletonTraits<EnhancedBookmarkModelFactory>;
+  friend struct base::DefaultSingletonTraits<EnhancedBookmarkModelFactory>;
 
   EnhancedBookmarkModelFactory();
   ~EnhancedBookmarkModelFactory() override;
 
   // BrowserStateKeyedServiceFactory implementation.
   scoped_ptr<KeyedService> BuildServiceInstanceFor(
       web::BrowserState* context) const override;
   web::BrowserState* GetBrowserStateToUse(
       web::BrowserState* context) const override;
 
   DISALLOW_COPY_AND_ASSIGN(EnhancedBookmarkModelFactory);
 };
 
 }  // namespace enhanced_bookmarks
 
 #endif  // IOS_CHROME_BROWSER_ENHANCED_BOOKMARKS_ENHANCED_BOOKMARK_MODEL_FACTORY_H_