Add exists, create and delete to directory implementation on Linux and Mac.

runtime/bin/directory.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.
 
 interface Directory factory _Directory {
   /**
    * Creates a directory object. The path is either a full path or
    * relative to the directory in which the Dart VM was
    * started.
    */
-  Directory(String dir);
+  Directory(String path);
+
+  /**
+   * Returns whether a directory with this name already exists.
+   */
+  bool exists();
+
+  /**
+   * Creates the directory with this name if it does not exist.
+   * Throw an exception if the directory already exists.
+   */
+  void create();
+
+  /**
+   * Deletes the directory with this name. Throws an exception
+   * if the directory is not empty or if deletion failed.
+   */
+  void delete();
 
   /**
    * List the sub-directories and files of this
    * [Directory]. Optionally recurse into sub-directories. For each
    * file and directory, the file or directory handler is called. When
    * all directories have been listed the done handler is called. If
    * the listing operation is recursive, the error handler is called
    * if a subdirectory cannot be opened for listing.
    */
   void list([bool recursive]);
@@ skipping 17 matching lines @@
    * done. The handler is called with an indication of whether or not
    * the listing operation completed.
    */
   void setDoneHandler(void doneHandler(bool completed));
 
   /**
    * Sets the error handler that is called on errors listing
    * directories.
    */
   void setErrorHandler(void errorHandler(String error));
+
+  /**
+   * Gets the path of this directory.
+   */
+  final String path;
 }