Fix error handling when current working directory is deleted.

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 extends FileSystemEntity implements Directory {
   static const CREATE_REQUEST = 0;
   static const DELETE_REQUEST = 1;
   static const EXISTS_REQUEST = 2;
   static const CREATE_TEMP_REQUEST = 3;
   static const LIST_START_REQUEST = 4;
   static const LIST_NEXT_REQUEST = 5;
   static const LIST_STOP_REQUEST = 6;
   static const RENAME_REQUEST = 7;
 
   final String path;
   SendPort _directoryService;
 
   _Directory(String this.path) {
     if (path is! String) {
       throw new ArgumentError('${Error.safeToString(path)} '
                               'is not a String');
     }
   }
 
-  external static String _current();
+  external static _current();
   external static _setCurrent(path);
   external static _createTemp(String template);
   external static int _exists(String path);
   external static _create(String path);
   external static _deleteNative(String path, bool recursive);
   external static _rename(String path, String newPath);
   external static List _list(String path, bool recursive, bool followLinks);
   external static SendPort _newServicePort();
 
-  static Directory get current => new _Directory(_current());
+  static Directory get current {
+    var result = _current();
+    if (result is OSError) {
+      throw new DirectoryException(
+          "Getting current working directory failed", "", result);
+    }
+    return new _Directory(result);
+  }
 
   static void set current(path) {
     if (path is Directory) path = path.path;
     var result = _setCurrent(path);
     if (result is ArgumentError) throw result;
     if (result is OSError) {
       throw new DirectoryException(
           "Setting current working directory failed", path, result);
     }
   }
@@ skipping 351 matching lines @@
       controller.addError(
           new DirectoryException("Directory listing failed",
                                  errorPath,
                                  err));
     } else {
       controller.addError(
           new DirectoryException("Internal error"));
     }
   }
 }