[ObjC ARC] Converts ios/chrome/browser/prefs:browser_prefs to ARC.

ios/chrome/browser/prefs/browser_prefs.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/prefs/browser_prefs.h"
 
 #include "components/autofill/core/browser/autofill_manager.h"
 #include "components/browsing_data/core/pref_names.h"
 #include "components/content_settings/core/browser/host_content_settings_map.h"
 #include "components/dom_distiller/core/distilled_page_prefs.h"
@@ skipping 37 matching lines @@
 #include "ios/chrome/browser/notification_promo.h"
 #include "ios/chrome/browser/physical_web/physical_web_prefs_registration.h"
 #include "ios/chrome/browser/pref_names.h"
 #include "ios/chrome/browser/signin/signin_manager_factory.h"
 #import "ios/chrome/browser/ui/bookmarks/bookmark_interaction_controller.h"
 #import "ios/chrome/browser/ui/bookmarks/bookmark_promo_controller.h"
 #include "ios/chrome/browser/voice/voice_search_prefs_registration.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #include "ui/base/l10n/l10n_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 void RegisterLocalStatePrefs(PrefRegistrySimple* registry) {
   BrowserStateInfoCache::RegisterPrefs(registry);
   flags_ui::PrefServiceFlagsStorage::RegisterPrefs(registry);
   gcm::GCMChannelStatusSyncer::RegisterPrefs(registry);
   ios::SigninManagerFactory::RegisterPrefs(registry);
   IOSChromeMetricsServiceClient::RegisterPrefs(registry);
   network_time::NetworkTimeTracker::RegisterPrefs(registry);
   ios::NotificationPromo::RegisterPrefs(registry);
   PrefProxyConfigTrackerImpl::RegisterPrefs(registry);
   rappor::RapporServiceImpl::RegisterPrefs(registry);
@@ skipping 94 matching lines @@
 }
 
 // This method should be periodically pruned of year+ old migrations.
 void MigrateObsoleteBrowserStatePrefs(PrefService* prefs) {
   // Added 07/2014.
   translate::TranslatePrefs::MigrateUserPrefs(prefs, prefs::kAcceptLanguages);
 
   // Added 08/2015.
   prefs->ClearPref(::prefs::kSigninSharedAuthenticationUserId);
 }