Make IOSink implement StringSink

tests/standalone/io/stdout_bad_argument_test.dart

Index: tests/standalone/io/stdout_bad_argument_test.dart
diff --git a/tests/standalone/io/stdout_bad_argument_test.dart b/tests/standalone/io/stdout_bad_argument_test.dart
index 95ce44d71b1a35b73023ef281a3835b870e513a1..481691f616d2a0c02ecdc6b1ff2163d27e07349b 100644
--- a/tests/standalone/io/stdout_bad_argument_test.dart
+++ b/tests/standalone/io/stdout_bad_argument_test.dart
@@ -1,11 +1,11 @@
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// 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";
 
 main() {
-  stdout.add("Hello\n");
+  stdout.writeBytes("Hello\n");
   stdout.done.catchError((e) {
     exit(0);
   });