Move Singleton and related structs to namespace base

ios/chrome/browser/autocomplete/shortcuts_backend_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/shortcuts_backend_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 36 matching lines @@
 // static
 scoped_refptr<ShortcutsBackend>
 ShortcutsBackendFactory::GetForBrowserStateIfExists(
     ios::ChromeBrowserState* browser_state) {
   return make_scoped_refptr(static_cast<ShortcutsBackend*>(
       GetInstance()->GetServiceForBrowserState(browser_state, false).get()));
 }
 
 // static
 ShortcutsBackendFactory* ShortcutsBackendFactory::GetInstance() {
-  return Singleton<ShortcutsBackendFactory>::get();
+  return base::Singleton<ShortcutsBackendFactory>::get();
 }
 
 ShortcutsBackendFactory::ShortcutsBackendFactory()
     : RefcountedBrowserStateKeyedServiceFactory(
           "ShortcutsBackend",
           BrowserStateDependencyManager::GetInstance()) {
   DependsOn(ios::HistoryServiceFactory::GetInstance());
   DependsOn(ios::TemplateURLServiceFactory::GetInstance());
 }
 
 ShortcutsBackendFactory::~ShortcutsBackendFactory() {}
 
 scoped_refptr<RefcountedKeyedService>
 ShortcutsBackendFactory::BuildServiceInstanceFor(
     web::BrowserState* context) const {
   ios::ChromeBrowserState* browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
   return CreateShortcutsBackend(browser_state, false /* suppress_db */);
 }
 
 bool ShortcutsBackendFactory::ServiceIsNULLWhileTesting() const {
   return true;
 }
 
 }  // namespace ios