Introduce PrefRegistrySyncable, simplifying PrefServiceSyncable.

chrome/browser/prefs/chrome_pref_service_factory.cc

Index: chrome/browser/prefs/chrome_pref_service_factory.cc
diff --git a/chrome/browser/prefs/chrome_pref_service_factory.cc b/chrome/browser/prefs/chrome_pref_service_factory.cc
index 39de2d18ac46e11478f6920345054f98c40b82a5..2307551f19298e04299c245f3b95d38dad9f7356 100644
--- a/chrome/browser/prefs/chrome_pref_service_factory.cc
+++ b/chrome/browser/prefs/chrome_pref_service_factory.cc
@@ -121,6 +121,7 @@ PrefServiceSyncable* CreateProfilePrefs(
     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,
@@ -129,7 +130,7 @@ PrefServiceSyncable* CreateProfilePrefs(
                  policy_service,
                  extension_prefs,
                  async);
-  return builder.CreateSyncable();
+  return builder.CreateSyncable(pref_registry);
 }
 
 }  // namespace chrome_prefs