Make IOSink implement StringSink

tests/standalone/io/process_std_io_script.dart

Index: tests/standalone/io/process_std_io_script.dart
diff --git a/tests/standalone/io/process_std_io_script.dart b/tests/standalone/io/process_std_io_script.dart
index 06ee29ad103abf30aeaf46909e2ee016d24ffc39..4ca28f40f73c74e128372f2f6f400c16a2f38af5 100644
--- a/tests/standalone/io/process_std_io_script.dart
+++ b/tests/standalone/io/process_std_io_script.dart
@@ -1,4 +1,4 @@
-// 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.
 //
@@ -15,8 +15,8 @@ main() {
       stdin.pipe(stderr);
     } else if (options.arguments[0] == "2") {
       stdin.listen((data) {
-        stdout.add(data);
-        stderr.add(data);
+        stdout.writeBytes(data);
+        stderr.writeBytes(data);
       });
     }
   }