Register delete time period pref for CBD on iOS

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"
 #include "components/flags_ui/pref_service_flags_storage.h"
 #include "components/gcm_driver/gcm_channel_status_syncer.h"
 #include "components/network_time/network_time_tracker.h"
 #include "components/ntp_snippets/ntp_snippets_service.h"
 #include "components/omnibox/browser/zero_suggest_provider.h"
 #include "components/password_manager/core/browser/password_manager.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/prefs/pref_service.h"
@@ skipping 113 matching lines @@
   // TODO(crbug.com/525079): those preferences are not used on iOS but are
   // required to be able to run unit_tests until componentization of
   // chrome/browser/prefs is complete.
   registry->RegisterListPref(kURLsToRestoreOnStartup,
                              user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   registry->RegisterListPref(kURLsToRestoreOnStartupOld);
 
   // Register prefs used by Clear Browsing Data UI.
   registry->RegisterIntegerPref(
       prefs::kClearBrowsingDataHistoryNoticeShownTimes, 0);
+  registry->RegisterIntegerPref(
+      browsing_data::prefs::kDeleteTimePeriod, 0,
+      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
 
   ios::GetChromeBrowserProvider()->RegisterProfilePrefs(registry);
 }
 
 // This method should be periodically pruned of year+ old migrations.
 void MigrateObsoleteLocalStatePrefs(PrefService* prefs) {
   // Added 05/2016.
   web_resource::PromoResourceService::ClearLocalState(prefs);
 }
 
 // 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);
 }