Report async errors when they happend, in directory listing.

sdk/lib/io/directory_impl.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.
 
 part of dart.io;
 
 class _Directory implements Directory {
   static const CREATE_REQUEST = 0;
   static const DELETE_REQUEST = 1;
   static const EXISTS_REQUEST = 2;
@@ skipping 264 matching lines @@
     if (_directoryService == null) {
       _directoryService = _newServicePort();
     }
   }
 
   final String _path;
   SendPort _directoryService;
 }
 
 class _AsyncDirectoryLister {
-  const int LIST_FILE = 0;
-  const int LIST_DIRECTORY = 1;
-  const int LIST_LINK = 2;
-  const int LIST_ERROR = 3;
-  const int LIST_DONE = 4;
+  static const int LIST_FILE = 0;
+  static const int LIST_DIRECTORY = 1;
+  static const int LIST_LINK = 2;
+  static const int LIST_ERROR = 3;
+  static const int LIST_DONE = 4;
 
-  const int RESPONSE_TYPE = 0;
-  const int RESPONSE_PATH = 1;
-  const int RESPONSE_COMPLETE = 1;
-  const int RESPONSE_ERROR = 2;
+  static const int RESPONSE_TYPE = 0;
+  static const int RESPONSE_PATH = 1;
+  static const int RESPONSE_COMPLETE = 1;
+  static const int RESPONSE_ERROR = 2;
 
   final String path;
   final bool recursive;
   final bool followLinks;
 
   StreamController controller;
   int id;
   bool canceled = false;
   bool nextRunning = false;
   bool closed = false;
@@ skipping 100 matching lines @@
       controller.addError(
           new DirectoryException("Directory listing failed",
                                  errorPath,
                                  err));
     } else {
       controller.addError(
           new DirectoryException("Internal error"));
     }
   }
 }