Fix type checking of void type.

runtime/bin/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.
 
 
 class _Directory implements Directory {
   static final CREATE_REQUEST = 0;
   static final DELETE_REQUEST = 1;
   static final EXISTS_REQUEST = 2;
   static final CREATE_TEMP_REQUEST = 3;
@@ skipping 70 matching lines @@
     request[1] = _path;
     return _directoryService.call(request).transform((response) {
       if (_isErrorResponse(response)) {
         throw _exceptionFromResponse(response,
                                      "Creation of temporary directory failed");
       }
       return new Directory(response);
     });
   }
 
-  void createTempSync() {
+  Directory createTempSync() {
     if (_path is !String) {
       throw new IllegalArgumentException();
     }
     var result = _createTemp(path);
     if (result is OSError) {
       throw new DirectoryIOException("Creation of temporary directory failed",
                                      _path,
                                      result);
     }
     return new Directory(result);
@@ skipping 183 matching lines @@
     } else {
       throw e;
     }
   }
 
   Function _onDir;
   Function _onFile;
   Function _onDone;
   Function _onError;
 }