Allow S->T <: dynamic->T

test/codegen/expect/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 869 matching lines @@
           } else {
             core.print(dart.dindex(msg, 'msg'));
           }
           break;
         case 'error':
           throw dart.dindex(msg, 'msg');
       }
     }
     static handleSpawnWorkerRequest(msg) {
       let replyPort = dart.dindex(msg, 'replyPort');
-      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$(core.String)), dart.dindex(msg, 'msg'), false, dart.as(dart.dindex(msg, 'isSpawnUri'), core.bool), dart.as(dart.dindex(msg, 'startPaused'), core.bool)).then((msg) => {
+      spawn(dart.as(dart.dindex(msg, 'functionName'), core.String), dart.as(dart.dindex(msg, 'uri'), core.String), dart.as(dart.dindex(msg, 'args'), core.List$(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) => {
         dart.dinvoke(replyPort, 'send', msg);
-      }, {
+      }, "(List<dynamic>) → dynamic"), {
         onError: (errorMessage) => {
           dart.dinvoke(replyPort, 'send', new 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 401 matching lines @@
   exports.globalWindow = globalWindow;
   exports.globalWorker = globalWorker;
   exports.globalPostMessageDefined = globalPostMessageDefined;
   exports.IsolateNatives = IsolateNatives;
   exports.RawReceivePortImpl = RawReceivePortImpl;
   exports.ReceivePortImpl = ReceivePortImpl;
   exports.TimerImpl = TimerImpl;
   exports.hasTimer = hasTimer;
   exports.CapabilityImpl = CapabilityImpl;
 })(_isolate_helper || (_isolate_helper = {}));