Add a mojo bridge for PersistentPrefStore.

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 d2e0d02510603c09e7a298e5134bd467ab045a1d..1420840c7d35afc18b307a3745aeec4feac07553 100644
--- a/chrome/browser/prefs/chrome_pref_service_factory.cc
+++ b/chrome/browser/prefs/chrome_pref_service_factory.cc
@@ -471,7 +471,7 @@ std::unique_ptr<PrefService> CreateLocalState(
 std::unique_ptr<sync_preferences::PrefServiceSyncable> CreateProfilePrefs(
     const base::FilePath& profile_path,
     base::SequencedTaskRunner* pref_io_task_runner,
-    TrackedPreferenceValidationDelegate* validation_delegate,
+    base::WeakPtr<TrackedPreferenceValidationDelegate> validation_delegate,
     policy::PolicyService* policy_service,
     SupervisedUserSettingsService* supervised_user_settings,
     const scoped_refptr<PrefStore>& extension_prefs,
@@ -493,9 +493,11 @@ std::unique_ptr<sync_preferences::PrefServiceSyncable> CreateProfilePrefs(
   sync_preferences::PrefServiceSyncableFactory factory;
   scoped_refptr<PersistentPrefStore> user_pref_store(
       CreateProfilePrefStoreManager(profile_path)
-          ->CreateProfilePrefStore(pref_io_task_runner,
-                                   start_sync_flare_for_prefs,
-                                   validation_delegate));
+          ->CreateProfilePrefStore(
+              content::BrowserThread::GetTaskRunnerForThread(
+                  content::BrowserThread::IO),
+              pref_io_task_runner, start_sync_flare_for_prefs,
+              validation_delegate));
   PrepareFactory(&factory, profile_path, policy_service,
                  supervised_user_settings, user_pref_store, extension_prefs,
                  async);