[ObjC ARC] Converts ios/chrome/browser/autocomplete to ARC.

ios/chrome/browser/autocomplete/shortcuts_backend_factory.mm

 // 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/ptr_util.h"
 #include "base/memory/singleton.h"
 #include "components/keyed_service/core/service_access_type.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "components/omnibox/browser/shortcuts_backend.h"
 #include "components/omnibox/browser/shortcuts_constants.h"
 #include "components/prefs/pref_service.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #include "ios/chrome/browser/history/history_service_factory.h"
 #include "ios/chrome/browser/pref_names.h"
 #include "ios/chrome/browser/search_engines/template_url_service_factory.h"
 #include "ios/chrome/browser/search_engines/ui_thread_search_terms_data.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #include "ios/web/public/web_thread.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace ios {
 namespace {
 
 scoped_refptr<ShortcutsBackend> CreateShortcutsBackend(
     ios::ChromeBrowserState* browser_state,
     bool suppress_db) {
   scoped_refptr<ShortcutsBackend> shortcuts_backend(new ShortcutsBackend(
       ios::TemplateURLServiceFactory::GetForBrowserState(browser_state),
       base::MakeUnique<ios::UIThreadSearchTermsData>(browser_state),
       ios::HistoryServiceFactory::GetForBrowserState(
@@ skipping 42 matching lines @@
   ios::ChromeBrowserState* browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
   return CreateShortcutsBackend(browser_state, false /* suppress_db */);
 }
 
 bool ShortcutsBackendFactory::ServiceIsNULLWhileTesting() const {
   return true;
 }
 
 }  // namespace ios