Move Singleton and related structs to namespace base

chrome/browser/enhanced_bookmarks/enhanced_bookmark_model_factory.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 CHROME_BROWSER_ENHANCED_BOOKMARKS_ENHANCED_BOOKMARK_MODEL_FACTORY_H_
 #define CHROME_BROWSER_ENHANCED_BOOKMARKS_ENHANCED_BOOKMARK_MODEL_FACTORY_H_
 
 #include "base/macros.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
+namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
+}  // namespace base
 
 namespace enhanced_bookmarks {
 
 class EnhancedBookmarkModel;
 
 // A factory to create one unique EnhancedBookmarkModel.
 class EnhancedBookmarkModelFactory : public BrowserContextKeyedServiceFactory {
  public:
   static EnhancedBookmarkModelFactory* GetInstance();
   static EnhancedBookmarkModel* GetForBrowserContext(
       content::BrowserContext* context);
 
  private:
-  friend struct DefaultSingletonTraits<EnhancedBookmarkModelFactory>;
+  friend struct base::DefaultSingletonTraits<EnhancedBookmarkModelFactory>;
 
   EnhancedBookmarkModelFactory();
   ~EnhancedBookmarkModelFactory() override {}
 
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
 
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
 
   DISALLOW_COPY_AND_ASSIGN(EnhancedBookmarkModelFactory);
 };
 
 }  // namespace enhanced_bookmarks
 
 #endif  // CHROME_BROWSER_ENHANCED_BOOKMARKS_ENHANCED_BOOKMARK_MODEL_FACTORY_H_