Move Singleton and related structs to namespace base

ios/chrome/browser/enhanced_bookmarks/enhanced_bookmark_model_factory.cc

 // 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.
 
 #include "ios/chrome/browser/enhanced_bookmarks/enhanced_bookmark_model_factory.h"
 
 #include "base/memory/singleton.h"
 #include "components/enhanced_bookmarks/enhanced_bookmark_model.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "components/version_info/version_info.h"
 #include "ios/chrome/browser/bookmarks/bookmark_model_factory.h"
 #include "ios/chrome/browser/browser_state/browser_state_otr_helper.h"
 #include "ios/public/provider/chrome/browser/browser_state/chrome_browser_state.h"
 
 namespace enhanced_bookmarks {
 
 // static
 EnhancedBookmarkModelFactory* EnhancedBookmarkModelFactory::GetInstance() {
-  return Singleton<EnhancedBookmarkModelFactory>::get();
+  return base::Singleton<EnhancedBookmarkModelFactory>::get();
 }
 
 // static
 EnhancedBookmarkModel* EnhancedBookmarkModelFactory::GetForBrowserState(
     ios::ChromeBrowserState* browser_state) {
   return static_cast<EnhancedBookmarkModel*>(
       GetInstance()->GetServiceForBrowserState(browser_state, true));
 }
 
 EnhancedBookmarkModelFactory::EnhancedBookmarkModelFactory()
@@ skipping 15 matching lines @@
       ios::BookmarkModelFactory::GetForBrowserState(browser_state),
       "chrome." + version_info::GetVersionNumber()));
 }
 
 web::BrowserState* EnhancedBookmarkModelFactory::GetBrowserStateToUse(
     web::BrowserState* context) const {
   return GetBrowserStateRedirectedInIncognito(context);
 }
 
 }  // namespace enhanced_bookmarks