Quiclk fix: it is a future.

tools/dom/src/Timer.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;
 
 // TODO(antonm): support not DOM isolates too.
 class _Timer implements Timer {
   final canceller;
 
@@ skipping 19 matching lines @@
 };
 
 class _PureIsolateTimer implements Timer {
   final ReceivePort _port = new ReceivePort();
   SendPort _sendPort; // Effectively final.
 
   _PureIsolateTimer(int milliSeconds, callback, repeating) {
     _sendPort = _port.toSendPort();
     _port.receive((msg, replyTo) {
       assert(msg == _TIMER_PING);
-      assert(replyTo == _HELPER_ISOLATE_PORT);
       callback(this);
       if (!repeating) _cancel();
     });
     _HELPER_ISOLATE_PORT.then((port) {
       port.send([_NEW_TIMER, milliSeconds, repeating], _sendPort);
     });
   }
 
   void cancel() {
     _cancel();
     _HELPER_ISOLATE_PORT.then((port) {
       port.send([_CANCEL_TIMER], _sendPort);
     });
   }
 
   void _cancel() {
     _port.close();
   }
 }
 
 get _pureIsolateTimerFactoryClosure =>
     ((int milliSeconds, void callback(Timer time), bool repeating) =>
         new _PureIsolateTimer(milliSeconds, callback, repeating));