Fixes memory leak of async directory lister

runtime/bin/directory_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 patch class _Directory {
   /* patch */ static _current() native "Directory_Current";
   /* patch */ static _setCurrent(path) native "Directory_SetCurrent";
   /* patch */ static _createTemp(String path) native "Directory_CreateTemp";
   /* patch */ static String _systemTemp() native "Directory_SystemTemp";
   /* patch */ static _exists(String path) native "Directory_Exists";
   /* patch */ static _create(String path) native "Directory_Create";
   /* patch */ static _deleteNative(String path, bool recursive)
       native "Directory_Delete";
   /* patch */ static _rename(String path, String newPath)
       native "Directory_Rename";
   /* patch */ static List _list(String path, bool recursive, bool followLinks)
       native "Directory_List";
 }
+
+patch class _AsyncDirectoryListerOps {
+  /* patch */ factory _AsyncDirectoryListerOps(int pointer) =>
+      new _AsyncDirectoryListerOpsImpl(pointer);
+}
+
+class _AsyncDirectoryListerOpsImpl extends NativeFieldWrapperClass1
+                                   implements _AsyncDirectoryListerOps {
+  _AsyncDirectoryListerOpsImpl._();
+
+  factory _AsyncDirectoryListerOpsImpl(int pointer)
+      => new _AsyncDirectoryListerOpsImpl._().._setPointer(pointer);
+
+  void _setPointer(int pointer)
+      native "Directory_SetAsyncDirectoryListerPointer";
+  int getPointer()
+      native "Directory_GetAsyncDirectoryListerPointer";
+}