dom: more final more of the time

tools/dom/src/Isolates.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.
 
 part of html;
 
 _serialize(var message) {
   return new _JsSerializer().traverse(message);
 }
 
@@ skipping 45 matching lines @@
         return ReceivePortSync._lookup(isolateId, portId);
       default:
         throw 'Illegal SendPortSync type: $tag';
     }
   }
 }
 
 // The receiver is JS.
 class _JsSendPortSync implements SendPortSync {
 
-  num _id;
+  final num _id;
   _JsSendPortSync(this._id);
 
   callSync(var message) {
     var serialized = _serialize(message);
     var result = _callPortSync(_id, serialized);
     return _deserialize(result);
   }
 
   bool operator==(var other) {
     return (other is _JsSendPortSync) && (_id == other._id);
@@ skipping 136 matching lines @@
 
 get _isolateId => ReceivePortSync._isolateId;
 
 void _dispatchEvent(String receiver, var message) {
   var event = new CustomEvent(receiver, canBubble: false, cancelable:false,
     detail: json.stringify(message));
   window.dispatchEvent(event);
 }
 
 String _getPortSyncEventData(CustomEvent event) => event.detail;