Added extension controlled prefs to TestingPrefService

This CL is extracted from https://codereview.chromium.org/2479113002.
to keep it under manageable size. This changes are helpful to emulate
extension controlled prefs in unit_tests.

[email protected]

Review-Url: https://codereview.chromium.org/2615403002
Cr-Commit-Position: refs/heads/master@{#442215}
diff --git a/components/sync_preferences/testing_pref_service_syncable.h b/components/sync_preferences/testing_pref_service_syncable.h
index 521b802..cf83573f 100644
--- a/components/sync_preferences/testing_pref_service_syncable.h
+++ b/components/sync_preferences/testing_pref_service_syncable.h
@@ -22,6 +22,7 @@
  public:
   TestingPrefServiceSyncable();
   TestingPrefServiceSyncable(TestingPrefStore* managed_prefs,
+                             TestingPrefStore* extension_prefs,
                              TestingPrefStore* user_prefs,
                              TestingPrefStore* recommended_prefs,
                              user_prefs::PrefRegistrySyncable* pref_registry,
@@ -45,6 +46,7 @@
 TestingPrefServiceBase<sync_preferences::PrefServiceSyncable,
                        user_prefs::PrefRegistrySyncable>::
     TestingPrefServiceBase(TestingPrefStore* managed_prefs,
+                           TestingPrefStore* extension_prefs,
                            TestingPrefStore* user_prefs,
                            TestingPrefStore* recommended_prefs,
                            user_prefs::PrefRegistrySyncable* pref_registry,