Don't wait unnecessarily.

compiler/lib/implementation/isolate_serialization.dart

 // Copyright (c) 2011, 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 MessageTraverser {
   static bool isPrimitive(x) {
     return (x === null) || (x is String) || (x is num) || (x is bool);
   }
 
   MessageTraverser();
@@ skipping 28 matching lines @@
   }
 
   _dispatch(var x) {
     if (isPrimitive(x)) return visitPrimitive(x);
     if (x is List) return visitList(x);
     if (x is Map) return visitMap(x);
     if (x is SendPortImpl) return visitSendPort(x);
     if (x is ReceivePortImpl) return visitReceivePort(x);
     if (x is ReceivePortSingleShotImpl) return visitReceivePortSingleShot(x);
     // TODO(floitsch): make this a real exception. (which one)?
-    throw "Message serialization: Illegal value $x passed";
+    throw new Exception("Message serialization: Illegal value $x passed");
   }
 
   abstract visitPrimitive(x);
   abstract visitList(List x);
   abstract visitMap(Map x);
   abstract visitSendPort(SendPortImpl x);
   abstract visitReceivePort(ReceivePortImpl x);
   abstract visitReceivePortSingleShot(ReceivePortSingleShotImpl x);
 
   List _taggedObjects;
@@ skipping 192 matching lines @@
     return a;
   }
 
   // TODO(floitsch): this should by Map<int, var> or Map<int, Dynamic>.
   Map _deserialized;
 
   static bool _isJsArray(x) native;
   static _jsArrayIndex(x, int index) native;
   static int _jsArrayLength(x) native;
 }