Move Singleton and related structs to namespace base

chrome/browser/notifications/extension_welcome_notification_factory.cc

 // 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.
 
 #include "chrome/browser/notifications/extension_welcome_notification_factory.h"
 
 #include "chrome/browser/notifications/extension_welcome_notification.h"
 #include "chrome/browser/notifications/notifier_state_tracker_factory.h"
 #include "chrome/browser/profiles/incognito_helpers.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "content/public/browser/browser_thread.h"
 
 // static
 ExtensionWelcomeNotification*
 ExtensionWelcomeNotificationFactory::GetForBrowserContext(
     content::BrowserContext* context) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   return static_cast<ExtensionWelcomeNotification*>(
       GetInstance()->GetServiceForBrowserContext(context, true));
 }
 
 // static
 ExtensionWelcomeNotificationFactory*
 ExtensionWelcomeNotificationFactory::GetInstance() {
-  return Singleton<ExtensionWelcomeNotificationFactory>::get();
+  return base::Singleton<ExtensionWelcomeNotificationFactory>::get();
 }
 
 ExtensionWelcomeNotificationFactory::ExtensionWelcomeNotificationFactory()
     : BrowserContextKeyedServiceFactory(
         "ExtensionWelcomeNotification",
         BrowserContextDependencyManager::GetInstance()) {
   DependsOn(NotifierStateTrackerFactory::GetInstance());
 }
 
 ExtensionWelcomeNotificationFactory::~ExtensionWelcomeNotificationFactory() {}
 
 KeyedService* ExtensionWelcomeNotificationFactory::BuildServiceInstanceFor(
     content::BrowserContext* context) const {
   return ExtensionWelcomeNotification::Create(static_cast<Profile*>(context));
 }
 
 content::BrowserContext*
 ExtensionWelcomeNotificationFactory::GetBrowserContextToUse(
     content::BrowserContext* context) const {
   return chrome::GetBrowserContextOwnInstanceInIncognito(context);
 }