Update dart:io to convert strings between UTF8 and current code page

tests/standalone/io/directory_non_ascii_sync_test.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.
+
+import 'dart:io';
+
+main() {
+  Directory scriptDir = new File(new Options().script).directorySync();
+  var d = new Directory("${scriptDir.path}/æøå");
+  Expect.isTrue(d.existsSync());
+  d.createSync();
+  var temp = new Directory('').createTempSync();
+  var temp2 = new Directory("${temp.path}/æøå").createTempSync();
+  Expect.isTrue(temp2.path.contains("æøå"));
+  temp2.deleteSync();
+  temp.deleteSync(recursive: true);
+}