Add the ability to change the working directory

sdk/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.
 
 part of dart.io;
 
 /**
  * [Directory] objects are used for working with directories.
  */
 abstract class Directory extends FileSystemEntity {
   /**
    * Creates a directory object. The path is either an absolute path,
    * or it is a relative path which is interpreted relative to the directory
    * in which the Dart VM was started.
    */
   factory Directory(String path) => new _Directory(path);
 
   /**
    * Creates a directory object from a Path object. The path is either
    * an absolute path, or it is a relative path which is interpreted
    * relative to the directory in which the Dart VM was started.
    */
   factory Directory.fromPath(Path path) => new _Directory.fromPath(path);
 
   /**
    * Creates a directory object pointing to the current working
    * directory.
    */
-  factory Directory.current() => new _Directory.current();
+  static Directory get current => _Directory.current;
+
+  /**
+   * Sets the current working directory of the Dart process including
+   * all running isolates. The new value set can be either a [Directory]
+   * or a [String].
+   *
+   * The new value is passed to the OS's system call unchanged, so a
+   * relative path passed as the new working directory will be
+   * resolved by the OS.
+   *
+   * Note that setting the current working directory is a synchronous
+   * operation and that it changes the the working directory of *all*
+   * isolates.
+   *
+   * Use this with care - especially when working with asynchronous
+   * operations and multiple isolates. Changing the working directory,
+   * while asynchronous operations are pending or when other isolates
+   * are working with the file system, can lead to unexpected results.
+   */
+  static void set current(path) {
+    _Directory.current = path;
+  }
 
   /**
    * Check whether a directory with this name already exists. Returns
    * a [:Future<bool>:] that completes with the result.
    */
   Future<bool> exists();
 
   /**
    * Synchronously check whether a directory with this name already exists.
    */
@@ skipping 179 matching lines @@
       if (path != null) {
         sb.write(", path = $path");
       }
     }
     return sb.toString();
   }
   final String message;
   final String path;
   final OSError osError;
 }