Disable closure wrapping by default

lib/runtime/dart/_isolate_helper.js

 var _isolate_helper;
 (function(exports) {
   'use strict';
   // Function _serializeMessage: (dynamic) → dynamic
   function _serializeMessage(message) {
     return new _Serializer().serialize(message);
   }
   // Function _deserializeMessage: (dynamic) → dynamic
   function _deserializeMessage(message) {
     return new _Deserializer().deserialize(message);
@@ skipping 934 matching lines @@
           break;
         }
         case 'error':
         {
           throw dart.dindex(msg, 'msg');
         }
       }
     }
     static handleSpawnWorkerRequest(msg) {
       let replyPort = dart.dindex(msg, 'replyPort');
-      IsolateNatives.spawn(dart.as(dart.dindex(msg, 'functionName'), core.String), dart.as(dart.dindex(msg, 'uri'), core.String), dart.as(dart.dindex(msg, 'args'), core.List$(core.String)), dart.dindex(msg, 'msg'), false, dart.as(dart.dindex(msg, 'isSpawnUri'), core.bool), dart.as(dart.dindex(msg, 'startPaused'), core.bool)).then(dart.closureWrap((msg) => {
+      IsolateNatives.spawn(dart.as(dart.dindex(msg, 'functionName'), core.String), dart.as(dart.dindex(msg, 'uri'), core.String), dart.as(dart.dindex(msg, 'args'), core.List$(core.String)), dart.dindex(msg, 'msg'), false, dart.as(dart.dindex(msg, 'isSpawnUri'), core.bool), dart.as(dart.dindex(msg, 'startPaused'), core.bool)).then(dart.as((msg) => {
         dart.dinvoke(replyPort, 'send', msg);
-      }, "(List<dynamic>) → dynamic"), {
+      }, dart.throw_("Unimplemented type (List<dynamic>) → dynamic")), {
         onError: (errorMessage) => {
           dart.dinvoke(replyPort, 'send', new core.List.from([_SPAWN_FAILED_SIGNAL, errorMessage]));
         }
       });
     }
     static [_log](msg) {
       if (exports._globalState.isWorker) {
         exports._globalState.mainManager.postMessage(_serializeMessage(dart.map({command: 'log', msg: msg})));
       } else {
         try {
@@ skipping 407 matching lines @@
   exports.leaveJsAsync = leaveJsAsync;
   exports.isWorker = isWorker;
   exports.startRootIsolate = startRootIsolate;
   exports.IsolateNatives = IsolateNatives;
   exports.RawReceivePortImpl = RawReceivePortImpl;
   exports.ReceivePortImpl = ReceivePortImpl;
   exports.TimerImpl = TimerImpl;
   exports.hasTimer = hasTimer;
   exports.CapabilityImpl = CapabilityImpl;
 })(_isolate_helper || (_isolate_helper = {}));