Move Singleton and related structs to namespace base

ios/chrome/browser/undo/bookmark_undo_service_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/undo/bookmark_undo_service_factory.h"
 
 #include "base/memory/singleton.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "components/undo/bookmark_undo_service.h"
 #include "ios/public/provider/chrome/browser/browser_state/chrome_browser_state.h"
 
 namespace ios {
 
 // static
 BookmarkUndoService* BookmarkUndoServiceFactory::GetForBrowserState(
     ios::ChromeBrowserState* browser_state) {
   return static_cast<BookmarkUndoService*>(
       GetInstance()->GetServiceForBrowserState(browser_state, true));
 }
 
 // static
 BookmarkUndoService* BookmarkUndoServiceFactory::GetForBrowserStateIfExists(
     ios::ChromeBrowserState* browser_state) {
   return static_cast<BookmarkUndoService*>(
       GetInstance()->GetServiceForBrowserState(browser_state, false));
 }
 
 // static
 BookmarkUndoServiceFactory* BookmarkUndoServiceFactory::GetInstance() {
-  return Singleton<BookmarkUndoServiceFactory>::get();
+  return base::Singleton<BookmarkUndoServiceFactory>::get();
 }
 
 BookmarkUndoServiceFactory::BookmarkUndoServiceFactory()
     : BrowserStateKeyedServiceFactory(
           "BookmarkUndoService",
           BrowserStateDependencyManager::GetInstance()) {
 }
 
 BookmarkUndoServiceFactory::~BookmarkUndoServiceFactory() {
 }
 
 scoped_ptr<KeyedService> BookmarkUndoServiceFactory::BuildServiceInstanceFor(
     web::BrowserState* context) const {
   return make_scoped_ptr(new BookmarkUndoService);
 }
 
 }  // namespace ios