Add the ability to change the working directory

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 "dart:isolate";
+
+import "package:expect/expect.dart";
+
+testChangeDirectory() {
+  var port = new ReceivePort();
+  new Directory("").createTemp().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());
+    Directory.current = "..";
+    Expect.isTrue(new File("111").existsSync());
+    Expect.isTrue(new File("222/333").existsSync());
+    Directory.current = initialCurrent;
+    temp.deleteSync(recursive: true);
+    port.close();
+  });
+}
+
+
+testChangeDirectoryIllegalArguments() {
+  Expect.throws(() => Directory.current = 1, (e) => e is ArgumentError);
+  Expect.throws(() => Directory.current = 111111111111111111111111111111111111,
+                (e) => e is ArgumentError);
+  Expect.throws(() => Directory.current = true, (e) => e is ArgumentError);
+  Expect.throws(() => Directory.current = [], (e) => e is ArgumentError);
+  Expect.throws(() => Directory.current = new File("xxx"),
+                (e) => e is ArgumentError);
+}
+
+
+main() {
+  testChangeDirectory();
+  testChangeDirectoryIllegalArguments();
+}