Improve the encoding/decoding to/from system encoding on Windows

tests/standalone/io/system_encoding_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.
+
+import 'dart:io';
+import 'dart:convert';
+
+import "package:expect/expect.dart";
+
+testEncodeDecode(str) {
+  Expect.equals(
+      SYSTEM_ENCODING.decoder.convert(
+          SYSTEM_ENCODING.encoder.convert(str)), str);
+}
+
+testDecodeEncode(bytes) {
+  Expect.listEquals(
+      SYSTEM_ENCODING.encoder.convert(
+          SYSTEM_ENCODING.decoder.convert(bytes)), bytes);
+}
+
+test(bytes) {

[kustermann, 2015/06/22 11:11:21]

Please add types to the parameters.

[Søren Gjesse, 2015/06/23 11:17:59]

Done.

+  var str = new String.fromCharCodes(bytes);
+  Expect.equals(SYSTEM_ENCODING.decoder.convert(bytes), str);
+  Expect.listEquals(SYSTEM_ENCODING.encoder.convert(str), bytes);
+  testDecodeEncode(bytes);
+  testEncodeDecode(str);
+}
+
+main() {
+  test([65, 66, 67]);
+  test([65, 0, 67]);
+  test([0, 65, 0, 67, 0]);
+  test([0, 0, 0]);
+  test(new Iterable.generate(128, (i) => i).toList());
+  testEncodeDecode('\u00c6\u00d8\u00c5');
+  if (Platform.isWindows) {
+    Expect.listEquals(
+        SYSTEM_ENCODING.encoder.convert('\u1234\u5678\u9abc'),
+        '???'.codeUnits);

[kustermann, 2015/06/22 11:11:21]

Could you add a comment here to explain the difference between windows and the
rest?

[Lasse Reichstein Nielsen, 2015/06/22 12:08:34]

WHat kind of silly encoding is that? :)

[Søren Gjesse, 2015/06/23 11:17:59]

That is what you get!

[Søren Gjesse, 2015/06/23 11:17:59]

Done.

+  } else {

[Lasse Reichstein Nielsen, 2015/06/22 12:08:34]

So all non-windows systems use UTF-8? So far. :)

[Søren Gjesse, 2015/06/23 11:17:59]

Yes, added comment.

+    Expect.listEquals(
+        SYSTEM_ENCODING.encoder.convert('\u1234\u5678\u9abc'),
+        UTF8.encoder.convert('\u1234\u5678\u9abc'));
+  }
+}