Add the ability to change the working directory

samples/build_dart/build.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.
 
 library build_dart;
 
 import "dart:io";
 import "package:args/args.dart";
 
 bool cleanBuild;
@@ skipping 54 matching lines @@
   useMachineInterface = args["machine"];
 
   cleanBuild = args["clean"];
   fullBuild = args["full"];
 }
 
 /**
  * Delete all generated files.
  */
 void handleCleanCommand() {
-  Directory current = new Directory.current();
+  Directory current = Directory.current;
   current.list(recursive: true).listen((FileSystemEntity entity) {
     if (entity is File) _maybeClean(entity);
   });
 }
 
 /**
  * Recursively scan the current directory looking for .foo files to process.
  */
 void handleFullBuild() {
   var files = <String>[];
 
-  new Directory.current().list(recursive: true).listen(
+  Directory.current.list(recursive: true).listen(
       (FileSystemEntity entity) {
         if (entity is File) files.add(entity.fullPathSync());
       },
       onDone: () => handleChangedFiles(files));
 }
 
 /**
  * Process the given list of changed files.
  */
 void handleChangedFiles(List<String> files) {
@@ skipping 50 matching lines @@
 }
 
 /**
  * If this file is a generated file (based on the extension), delete it.
  */
 void _maybeClean(File file) {
   if (file.path.endsWith(".foobar")) {
     file.delete();
   }
 }