[iOS] Remove support for asynchronous pref creation.

ios/chrome/browser/prefs/ios_chrome_pref_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/prefs/ios_chrome_pref_service_factory.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 15 matching lines @@
 // Record PersistentPrefStore's reading errors distribution.
 void HandleReadError(PersistentPrefStore::PrefReadError error) {
   // Sample the histogram also for the successful case in order to get a
   // baseline on the success rate in addition to the error distribution.
   UMA_HISTOGRAM_ENUMERATION("PrefService.ReadError", error,
                             PersistentPrefStore::PREF_READ_ERROR_MAX_ENUM);
 }
 
 void PrepareFactory(syncable_prefs::PrefServiceSyncableFactory* factory,
                     const base::FilePath& pref_filename,
-                    base::SequencedTaskRunner* pref_io_task_runner,
-                    bool async) {
+                    base::SequencedTaskRunner* pref_io_task_runner) {
   factory->set_user_prefs(make_scoped_refptr(new JsonPrefStore(
       pref_filename, pref_io_task_runner, scoped_ptr<PrefFilter>())));
 
-  factory->set_async(async);
   factory->set_read_error_callback(base::Bind(&HandleReadError));
   factory->SetPrefModelAssociatorClient(
       IOSChromePrefModelAssociatorClient::GetInstance());
 }
 
 }  // namespace
 
 scoped_ptr<PrefService> CreateLocalState(
     const base::FilePath& pref_filename,
     base::SequencedTaskRunner* pref_io_task_runner,
-    const scoped_refptr<PrefRegistry>& pref_registry,
-    bool async) {
+    const scoped_refptr<PrefRegistry>& pref_registry) {
   syncable_prefs::PrefServiceSyncableFactory factory;
-  PrepareFactory(&factory, pref_filename, pref_io_task_runner, async);
+  PrepareFactory(&factory, pref_filename, pref_io_task_runner);
   return factory.Create(pref_registry.get());
 }
 
 scoped_ptr<syncable_prefs::PrefServiceSyncable> CreateBrowserStatePrefs(
     const base::FilePath& browser_state_path,
     base::SequencedTaskRunner* pref_io_task_runner,
     TrackedPreferenceValidationDelegate* validation_delegate,
-    const scoped_refptr<user_prefs::PrefRegistrySyncable>& pref_registry,
-    bool async) {
+    const scoped_refptr<user_prefs::PrefRegistrySyncable>& pref_registry) {
   // chrome_prefs::CreateProfilePrefs uses ProfilePrefStoreManager to create
   // the preference store however since Chrome on iOS does not need to track
   // preference modifications (as applications are sand-boxed), it can use a
   // simple JsonPrefStore to store them (which is what PrefStoreManager uses
   // on platforms that do not track preference modifications).
   syncable_prefs::PrefServiceSyncableFactory factory;
   PrepareFactory(&factory, browser_state_path.Append(kPreferencesFilename),
-                 pref_io_task_runner, async);
+                 pref_io_task_runner);
   scoped_ptr<syncable_prefs::PrefServiceSyncable> pref_service =
       factory.CreateSyncable(pref_registry.get());
   ConfigureDefaultSearchPrefMigrationToDictionaryValue(pref_service.get());
   return pref_service.Pass();
 }
 
 scoped_ptr<syncable_prefs::PrefServiceSyncable>
 CreateIncognitoBrowserStatePrefs(
     syncable_prefs::PrefServiceSyncable* pref_service) {
   // List of keys that cannot be changed in the user prefs file by the incognito
   // browser state. All preferences that store information about the browsing
   // history or behaviour of the user should have this property.
   std::vector<const char*> overlay_pref_names;
   overlay_pref_names.push_back(proxy_config::prefs::kProxy);
   return make_scoped_ptr(pref_service->CreateIncognitoPrefService(
       nullptr,  // incognito_extension_pref_store
       overlay_pref_names));
 }