Modify tests to use Directory.systemTemp

tests/standalone/io/directory_chdir_test.dart

 // Copyright (c) 2013, 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 listing test.
 
 
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 testChangeDirectory() {
   asyncStart();
-  new Directory("").createTemp().then((temp) {
+  Directory.systemTemp.createTemp('dart_directory_chdir').then((temp) {
     var initialCurrent = Directory.current;
     Directory.current = temp;
     var newCurrent = Directory.current;
     new File("111").createSync();
     var dir = new Directory(newCurrent.path + Platform.pathSeparator + "222");
     dir.createSync();
     Directory.current = dir;
     new File("333").createSync();
     Expect.isTrue(new File("333").existsSync());
     Expect.isTrue(new File("../111").existsSync());
@@ skipping 22 matching lines @@
   Expect.throws(() => Directory.current = [], (e) => e is ArgumentError);
   Expect.throws(() => Directory.current = new File("xxx"),
                 (e) => e is ArgumentError);
 }
 
 
 main() {
   testChangeDirectory();
   testChangeDirectoryIllegalArguments();
 }