Make IOSink implement StringSink

tests/standalone/debugger/debug_lib.dart

Index: tests/standalone/debugger/debug_lib.dart
diff --git a/tests/standalone/debugger/debug_lib.dart b/tests/standalone/debugger/debug_lib.dart
index d71f3e64310b34dbbbcba321bd880e2431c1cc80..fbfcc78ecd6f08e918fcffcb1eaff97c45d31c8e 100644
--- a/tests/standalone/debugger/debug_lib.dart
+++ b/tests/standalone/debugger/debug_lib.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.
 
@@ -460,7 +460,7 @@ class Debugger {
   void sendMessage(Map<String,dynamic> msg) {
     String jsonMsg = JSON.stringify(msg);
     if (verboseWire) print("SEND: $jsonMsg");
-    socket.addString(jsonMsg);
+    socket.write(jsonMsg);
   }
 
   bool get errorsDetected => errors.length > 0;