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

tests/standalone/io/file_non_ascii_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';
+import 'dart:isolate';
+
+main() {
+  var port = new ReceivePort();
+  Directory scriptDir = new File(new Options().script).directorySync();
+  var f = new File("${scriptDir.path}/æøå/æøå.dat");
+  f.exists().then((e) {
+    Expect.isTrue(e);
+    f.create().then((_) {
+      f.directory().then((d) {
+        Expect.isTrue(d.path.endsWith('æøå'));
+        f.length().then((l) {
+          Expect.equals(6, l);
+          f.lastModified().then((_) {
+            f.fullPath().then((p) {
+              Expect.isTrue(p.endsWith('æøå.dat'));
+              f.readAsText().then((contents) {
+                Expect.equals('æøå', contents);
+                port.close();
+              });
+            });
+          });
+        });
+      });
+    });
+  });
+}