Very simple version of Isolates.

runtime/bin/io_service_patch.dart

Index: runtime/bin/io_service_patch.dart
diff --git a/runtime/bin/io_service_patch.dart b/runtime/bin/io_service_patch.dart
index c6a703529cf9fd67fe50451879e337ca6c48ae44..8f5a593055d923a75c26941b1f75f1a34000dbe4 100644
--- a/runtime/bin/io_service_patch.dart
+++ b/runtime/bin/io_service_patch.dart
@@ -30,13 +30,14 @@ patch class _IOService {
     }
     if (_receivePort == null) {
       _receivePort = new ReceivePort();
-      _replyToPort = _receivePort.toSendPort();
-      _receivePort.receive((data, _) {
+      _replyToPort = _receivePort.sendPort;
+      StreamSubscription subscription;
+      subscription = _receivePort.listen((data) {
         assert(data is List && data.length == 2);
         _messageMap.remove(data[0]).complete(data[1]);
         if (_messageMap.length == 0) {
           _id = 0;
-          _receivePort.close();
+          subscription.cancel();
           _receivePort = null;
         }
       });