Migrate test block 5 to Dart 2.0.

tests/corelib_strong/date_time8_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 "package:expect/expect.dart";
-
-// Make sure the year 0 is correctly printed.
-
-testUtc() {
-  var d = new DateTime.utc(0, 1, 1);
-  Expect.equals("0000-01-01 00:00:00.000Z", d.toString());
-}
-
-testLocal() {
-  var d = new DateTime(0, 1, 1);
-  Expect.equals("0000-01-01 00:00:00.000", d.toString());
-}
-
-main() {
-  testUtc();
-  testLocal();
-}