[dart:io] Adds Platform.ansiSupported

tests/standalone/io/ansi_supported_test.dart

Index: tests/standalone/io/ansi_supported_test.dart
diff --git a/tests/standalone/io/ansi_supported_test.dart b/tests/standalone/io/ansi_supported_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..a0f46690eb06907ace8062ae3f8611e0ec15e52a
--- /dev/null
+++ b/tests/standalone/io/ansi_supported_test.dart
@@ -0,0 +1,23 @@
+// 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.
+
+import 'dart:io';
+
+import "package:expect/expect.dart";
+
+main() {
+  try {
+    Platform.ansiSupported;
+  } catch (e, s) {
+    Expect.fail("Platform.ansiSupported threw: $e\n$s\n");
+  }
+  Expect.isNotNull(Platform.ansiSupported);
+  Expect.isTrue(Platform.ansiSupported is bool);
+  if (stdout.hasTerminal && Platform.ansiSupported) {
+    stdout.writeln('\x1b[31mThis text has a red foreground using SGR.31.');
+    stdout.writeln('\x1b[39mThis text has restored the foreground color.');
+  } else {
+    stdout.writeln('ANSI codes not supported on this platform');
+  }
+}