Use native wrapper fields to store socket ids.

runtime/bin/timer_impl.dart

 // 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.
 
 class _Timer implements Timer {
   // Set jitter to wake up timer events that would happen in _TIMER_JITTER ms.
   static const int _TIMER_JITTER = 0;
 
   // Disables the timer.
   static const int _NO_TIMER = -1;
@@ skipping 81 matching lines @@
       // While we are already handling callbacks we will not notify the event
       // handler. _handleTimeout will call _notifyEventHandler once all pending
       // timers are processed.
       return;
     }
 
     if (_timers.firstEntry() === null) {
       // No pending timers: Close the receive port and let the event handler
       // know.
       if (_receivePort !== null) {
-        _EventHandler._sendData(-1, _receivePort, _NO_TIMER);
+        _EventHandler._sendData(null, _receivePort, _NO_TIMER);
         _shutdownTimerHandler();
       }
     } else {
       if (_receivePort === null) {
         // Create a receive port and register a message handler for the timer
         // events.
         _createTimerHandler();
       }
-      _EventHandler._sendData(-1,
+      _EventHandler._sendData(null,
                               _receivePort,
                               _timers.firstEntry().element._wakeupTime);
     }
   }
 
 
   // Creates a receive port and registers the timer handler on that
   // receive port.
   void _createTimerHandler() {
 
@@ skipping 69 matching lines @@
 _getTimerFactoryClosure() {
   return (int milliSeconds, void callback(Timer timer), bool repeating) {
     if (repeating) {
       return new _Timer.repeating(milliSeconds, callback);
     }
     return new _Timer(milliSeconds, callback);
   };
 }