Move Singleton and related structs to namespace base

ios/chrome/browser/dom_distiller/dom_distiller_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/dom_distiller/dom_distiller_service_factory.h"
 
 #include "base/files/file_path.h"
 #include "base/memory/singleton.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "components/dom_distiller/core/article_entry.h"
@@ skipping 31 matching lines @@
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DomDistillerKeyedService);
 };
 }  // namespace
 
 namespace dom_distiller {
 
 // static
 DomDistillerServiceFactory* DomDistillerServiceFactory::GetInstance() {
-  return Singleton<DomDistillerServiceFactory>::get();
+  return base::Singleton<DomDistillerServiceFactory>::get();
 }
 
 // static
 DomDistillerService* DomDistillerServiceFactory::GetForBrowserState(
     ios::ChromeBrowserState* browser_state) {
   return static_cast<DomDistillerKeyedService*>(
       GetInstance()->GetServiceForBrowserState(browser_state, true));
 }
 
 DomDistillerServiceFactory::DomDistillerServiceFactory()
@@ skipping 37 matching lines @@
       distiller_page_factory.Pass(), distilled_page_prefs.Pass()));
 }
 
 web::BrowserState* DomDistillerServiceFactory::GetBrowserStateToUse(
     web::BrowserState* context) const {
   // Makes normal profile and off-the-record profile use same service instance.
   return GetBrowserStateRedirectedInIncognito(context);
 }
 
 }  // namespace dom_distiller