Introduce PrefRegistrySyncable, simplifying PrefServiceSyncable.

chrome/browser/prefs/chrome_pref_service_factory.cc

 // Copyright (c) 2012 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 "chrome/browser/prefs/chrome_pref_service_factory.h"
 
 #include "base/bind.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/metrics/histogram.h"
@@ skipping 103 matching lines @@
                  extension_prefs,
                  async);
   return builder.Create(pref_registry);
 }
 
 PrefServiceSyncable* CreateProfilePrefs(
     const FilePath& pref_filename,
     base::SequencedTaskRunner* pref_io_task_runner,
     policy::PolicyService* policy_service,
     const scoped_refptr<PrefStore>& extension_prefs,
+    const scoped_refptr<PrefRegistrySyncable>& pref_registry,
     bool async) {
   PrefServiceSyncableBuilder builder;
   PrepareBuilder(&builder,
                  pref_filename,
                  pref_io_task_runner,
                  policy_service,
                  extension_prefs,
                  async);
-  return builder.CreateSyncable();
+  return builder.CreateSyncable(pref_registry);
 }
 
 }  // namespace chrome_prefs