[iOS] Remove support for asynchronous pref creation.

ios/chrome/browser/prefs/ios_chrome_pref_service_factory.h

Index: ios/chrome/browser/prefs/ios_chrome_pref_service_factory.h
diff --git a/ios/chrome/browser/prefs/ios_chrome_pref_service_factory.h b/ios/chrome/browser/prefs/ios_chrome_pref_service_factory.h
index 5971ab21269ae64a7d113065de41303366abebe7..7e4b610bbf61cd955294ba9bf1799d429cf81e1a 100644
--- a/ios/chrome/browser/prefs/ios_chrome_pref_service_factory.h
+++ b/ios/chrome/browser/prefs/ios_chrome_pref_service_factory.h
@@ -34,19 +34,17 @@ class PrefRegistrySyncable;
 // for Chrome on iOS with the applicable PrefStores. The |pref_filename| points
 // to the user preference file. This is the usual way to create a new
 // PrefService. |pref_registry| keeps the list of registered prefs and their
-// default valuers. If |async| is true, asynchronous version is used.
+// default values.
 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);
 
 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);
 
 // Creates an incognito copy of |pref_service| that shares most prefs but uses
 // a fresh non-persistent overlay for the user pref store.