[Sync] Remove backend unrecoverable error handler

sync/internal_api/sync_rollback_manager_base.h

Index: sync/internal_api/sync_rollback_manager_base.h
diff --git a/sync/internal_api/sync_rollback_manager_base.h b/sync/internal_api/sync_rollback_manager_base.h
index ef09c4e8de99f8e4d9f6aa54a77220d69136d28c..638b2f063d053bae07c521441f812fa9fb3a1d82 100644
--- a/sync/internal_api/sync_rollback_manager_base.h
+++ b/sync/internal_api/sync_rollback_manager_base.h
@@ -100,7 +100,7 @@ class SYNC_EXPORT_PRIVATE SyncRollbackManagerBase :
       const base::FilePath& database_location,
       InternalComponentsFactory* internal_components_factory,
       InternalComponentsFactory::StorageOption storage,
-      scoped_ptr<UnrecoverableErrorHandler> unrecoverable_error_handler,
+      const WeakHandle<UnrecoverableErrorHandler>& unrecoverable_error_handler,
       const base::Closure& report_unrecoverable_error_function);
 
   void RegisterDirectoryTypeDebugInfoObserver(
@@ -129,7 +129,7 @@ class SYNC_EXPORT_PRIVATE SyncRollbackManagerBase :
   UserShare share_;
   base::ObserverList<SyncManager::Observer> observers_;
 
-  scoped_ptr<UnrecoverableErrorHandler> unrecoverable_error_handler_;
+  WeakHandle<UnrecoverableErrorHandler> unrecoverable_error_handler_;
   base::Closure report_unrecoverable_error_function_;
 
   scoped_ptr<SyncEncryptionHandler> dummy_handler_;