Make IOSink implement StringSink

tests/standalone/io/file_system_links_test.dart

Index: tests/standalone/io/file_system_links_test.dart
diff --git a/tests/standalone/io/file_system_links_test.dart b/tests/standalone/io/file_system_links_test.dart
index 3179d7df0b4fc80e5fd8415d4604bb57ff06e366..25babf1282c445d298a84a61a99b81a7937fa3a4 100644
--- a/tests/standalone/io/file_system_links_test.dart
+++ b/tests/standalone/io/file_system_links_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.
 
@@ -104,8 +104,8 @@ testFileWriteRead() {
   new File(x).createSync();
   createLink(x, y, true, () {
     var data = "asdf".codeUnits;
-    var output = new File(y).openWrite(FileMode.WRITE);
-    output.add(data);
+    var output = new File(y).openWrite(mode: FileMode.WRITE);
+    output.writeBytes(data);
     output.close();
     output.done.then((_) {
       var read = new File(y).readAsBytesSync();