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

tests/standalone/io/file_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 f = new File("${scriptDir.path}/æøå/æøå.dat");
+  Expect.isTrue(f.existsSync());
+  f.createSync();
+  Expect.isTrue(f.directorySync().path.endsWith('æøå'));;
+  Expect.equals(6, f.lengthSync());
+  f.lastModifiedSync();
+  Expect.isTrue(f.fullPathSync().endsWith('æøå.dat'));
+  Expect.equals('æøå', f.readAsTextSync());
+}