Post on the error handler in the Directory API when errors are encountered.

runtime/bin/directory_impl.dart

 // Copyright (c) 2011, 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.
 
 
 class _DirectoryListingIsolate extends Isolate {
 
   _DirectoryListingIsolate() : super.heavy();
 
   void main() {
@@ skipping 18 matching lines @@
 }
 
 
 class _Directory implements Directory {
 
   _Directory(String this._path);
 
   bool existsSync() {
     int exists = _exists(_path);
     if (exists < 0) {
-      // TODO(ager): Supply a better error message.
       throw new DirectoryException("Diretory exists test failed: $_path");
     }
     return (exists == 1);
   }
 
   void createSync() {
     if (!_create(_path)) {
-      // TODO(ager): Supply a better error message.
       throw new DirectoryException("Directory creation failed: $_path");
     }
   }
 
   void deleteSync() {
     if (!_delete(_path)) {
-      // TODO(ager): Supply a better error message.
       throw new DirectoryException("Directory deletion failed: $_path");
     }
   }
 
   void list([bool recursive = false]) {
     new _DirectoryListingIsolate().spawn().then((port) {
       // Build a map of parameters to the directory listing isolate.
       Map listingParameters = new Map();
       listingParameters['dir'] = _path;
       listingParameters['recursive'] = recursive;
@@ skipping 83 matching lines @@
   bool _create(String path) native "Directory_Create";
   bool _delete(String path) native "Directory_Delete";
 
   var _dirHandler;
   var _fileHandler;
   var _doneHandler;
   var _errorHandler;
 
   String _path;
 }