Use native wrapper fields to store socket ids.

runtime/bin/eventhandler.dart

Index: runtime/bin/eventhandler.dart
diff --git a/runtime/bin/eventhandler.dart b/runtime/bin/eventhandler.dart
index 8310a0a9d2373a9bf5c54121d53fd103deeb2c08..2e0a8fc1910a626b6d5e1dbec68331c966670193 100644
--- a/runtime/bin/eventhandler.dart
+++ b/runtime/bin/eventhandler.dart
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, 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.
 
@@ -14,13 +14,13 @@ class _EventHandler extends NativeFieldWrapperClass1 {
 
   void _doStart() native "EventHandler_Start";
 
-  static _sendData(int id, ReceivePort receivePort, int data) {
+  static _sendData(Object sender, ReceivePort receivePort, int data) {
     if (_eventHandler !== null) {
-      _eventHandler._doSendData(id, receivePort, data);
+      _eventHandler._doSendData(sender, receivePort, data);
     }
   }
 
-  void _doSendData(int id, ReceivePort receivePort, int data)
+  void _doSendData(Object sender, ReceivePort receivePort, int data)
       native "EventHandler_SendData";
 
   static _EventHandler _eventHandler;