Move Singleton and related structs to namespace base

ios/chrome/browser/history/web_history_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/history/web_history_service_factory.h"
 
 #include "base/memory/singleton.h"
 #include "base/prefs/pref_service.h"
 #include "components/history/core/browser/web_history_service.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
@@ skipping 28 matching lines @@
   // signed into sync, or if web history is not enabled.
   if (!IsHistorySyncEnabled(browser_state))
     return nullptr;
 
   return static_cast<history::WebHistoryService*>(
       GetInstance()->GetServiceForBrowserState(browser_state, true));
 }
 
 // static
 WebHistoryServiceFactory* WebHistoryServiceFactory::GetInstance() {
-  return Singleton<WebHistoryServiceFactory>::get();
+  return base::Singleton<WebHistoryServiceFactory>::get();
 }
 
 WebHistoryServiceFactory::WebHistoryServiceFactory()
     : BrowserStateKeyedServiceFactory(
           "WebHistoryService",
           BrowserStateDependencyManager::GetInstance()) {
   ios::KeyedServiceProvider* provider = ios::GetKeyedServiceProvider();
   DependsOn(provider->GetSyncServiceFactory());
   DependsOn(OAuth2TokenServiceFactory::GetInstance());
   DependsOn(ios::SigninManagerFactory::GetInstance());
 }
 
 WebHistoryServiceFactory::~WebHistoryServiceFactory() {
 }
 
 scoped_ptr<KeyedService> WebHistoryServiceFactory::BuildServiceInstanceFor(
     web::BrowserState* context) const {
   ios::ChromeBrowserState* browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
   return make_scoped_ptr(new history::WebHistoryService(
       OAuth2TokenServiceFactory::GetForBrowserState(browser_state),
       ios::SigninManagerFactory::GetForBrowserState(browser_state),
       browser_state->GetRequestContext()));
 }
 
 }  // namespace ios