[test.dart] Complain if there is non-utf8 formatted data in test output

tests/standalone/io/non_utf8_output_test.dart

Index: tests/standalone/io/non_utf8_output_test.dart
diff --git a/tests/standalone/io/non_utf8_output_test.dart b/tests/standalone/io/non_utf8_output_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..0e10a292e059b93e8a708d6fe5a7d1f7217588be
--- /dev/null
+++ b/tests/standalone/io/non_utf8_output_test.dart
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+// Copyright (c) 2017, 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.
+
+// This test emits non-UTF8 formatted data.
+// It should have the test expectation: NonUtf8Output.
+
+import 'dart:io';
+
+main() {
+  String german = "German characters: aäbcdefghijklmnoöpqrsßtuüvwxyz";
+  stdout.add(german.runes.toList());
+}