Adds async interface method to PersistentPrefStore.

chrome/test/testing_pref_service.cc

Index: chrome/test/testing_pref_service.cc
diff --git a/chrome/test/testing_pref_service.cc b/chrome/test/testing_pref_service.cc
index 6d792b9b131d757766280856564995037453ef5d..e9516ab823ea7d04f8a7371e7a3a033dddf72b95 100644
--- a/chrome/test/testing_pref_service.cc
+++ b/chrome/test/testing_pref_service.cc
@@ -25,8 +25,7 @@ TestingPrefServiceBase::TestingPrefServiceBase(
                   user_prefs,
                   recommended_platform_prefs,
                   NULL,
-                  new DefaultPrefStore(),
-                  NULL),
+                  new DefaultPrefStore()),
       managed_platform_prefs_(managed_platform_prefs),
       user_prefs_(user_prefs),
       recommended_platform_prefs_(recommended_platform_prefs) {
@@ -111,4 +110,3 @@ ScopedTestingLocalState::~ScopedTestingLocalState() {
   EXPECT_EQ(&local_state_, browser_process_->local_state());
   browser_process_->SetLocalState(NULL);
 }
-