Make IOSink implement StringSink

tests/standalone/io/stream_pipe_test.dart

Index: tests/standalone/io/stream_pipe_test.dart
diff --git a/tests/standalone/io/stream_pipe_test.dart b/tests/standalone/io/stream_pipe_test.dart
index 46590fa348178412e7db304f56108e394072b2ae..e2b995c012d8de652938adc026eb9a20e1c86bf3 100644
--- a/tests/standalone/io/stream_pipe_test.dart
+++ b/tests/standalone/io/stream_pipe_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.
 //
@@ -100,7 +100,7 @@ testFileToFilePipe2() {
   dstFile.createSync();
   var output = dstFile.openWrite();
   output.addStream(srcStream).then((_) {
-    output.add([32]);
+    output.writeBytes([32]);
     output.close();
     output.done.then((_) {
       var src = srcFile.openSync();