Move Singleton and related structs to namespace base

ios/chrome/browser/autocomplete/in_memory_url_index_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/autocomplete/in_memory_url_index_factory.h"
 
 #include "base/memory/singleton.h"
 #include "base/prefs/pref_service.h"
 #include "components/keyed_service/core/service_access_type.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
@@ skipping 10 matching lines @@
 
 // static
 InMemoryURLIndex* InMemoryURLIndexFactory::GetForBrowserState(
     ios::ChromeBrowserState* browser_state) {
   return static_cast<InMemoryURLIndex*>(
       GetInstance()->GetServiceForBrowserState(browser_state, true));
 }
 
 // static
 InMemoryURLIndexFactory* InMemoryURLIndexFactory::GetInstance() {
-  return Singleton<InMemoryURLIndexFactory>::get();
+  return base::Singleton<InMemoryURLIndexFactory>::get();
 }
 
 InMemoryURLIndexFactory::InMemoryURLIndexFactory()
     : BrowserStateKeyedServiceFactory(
           "InMemoryURLIndex",
           BrowserStateDependencyManager::GetInstance()) {
   DependsOn(ios::BookmarkModelFactory::GetInstance());
   DependsOn(ios::HistoryServiceFactory::GetInstance());
 }
 
@@ skipping 23 matching lines @@
 web::BrowserState* InMemoryURLIndexFactory::GetBrowserStateToUse(
     web::BrowserState* context) const {
   return GetBrowserStateRedirectedInIncognito(context);
 }
 
 bool InMemoryURLIndexFactory::ServiceIsNULLWhileTesting() const {
   return true;
 }
 
 }  // namespace ios