Make IOSink implement StringSink

tests/standalone/io/secure_socket_bad_certificate_test.dart

Index: tests/standalone/io/secure_socket_bad_certificate_test.dart
diff --git a/tests/standalone/io/secure_socket_bad_certificate_test.dart b/tests/standalone/io/secure_socket_bad_certificate_test.dart
index 3f2b3200363c5e2ac002f583109f63e6e0fd7f90..c2581f82011860c2e2be3650c98fc24dfce3bc0e 100644
--- a/tests/standalone/io/secure_socket_bad_certificate_test.dart
+++ b/tests/standalone/io/secure_socket_bad_certificate_test.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.
 //
@@ -49,7 +49,7 @@ Future testCertificateCallback({String host, bool acceptCertificate}) {
                               onBadCertificate: badCertificateCallback)
       .then((socket) {
         Expect.isTrue(acceptCertificate);
-        socket.add("GET / HTTP/1.0\r\nHost: $host\r\n\r\n".codeUnits);
+        socket.write("GET / HTTP/1.0\r\nHost: $host\r\n\r\n");
         socket.close();
         return socket.reduce(<int>[], (message, data)  => message..addAll(data))
             .then((message) {