Use patching for dart:io.

lib/io/directory.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.
 
 /**
  * [Directory] objects are used for working with directories.
  */
 abstract class Directory {
   /**
    * Creates a directory object. The path is either an absolute path,
@@ skipping 184 matching lines @@
       if (path != null) {
         sb.add(", path = $path");
       }
     }
     return sb.toString();
   }
   final String message;
   final String path;
   final OSError osError;
 }