Asyncstar - exception thrown before yield or await would not get caught

sdk/lib/_internal/compiler/js_lib/js_helper.dart

 // Copyright (c) 2013, 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.
 
 library _js_helper;
 
 import 'dart:_async_await_error_codes' as async_error_codes;
 
 import 'dart:_js_embedded_names' show
     JsGetName,
@@ skipping 3711 matching lines @@
   bool stopRunning = false;
   bool isAdding = false;
   bool get isPaused => controller.isPaused;
   add(event) => controller.add(event);
   addStream(Stream stream) {
     return controller.addStream(stream, cancelOnError: false);
   }
   addError(error, stackTrace) => controller.addError(error, stackTrace);
   close() => controller.close();
 
-  AsyncStarStreamController(helperCallback) {
+  AsyncStarStreamController(body) {
     controller = new StreamController(
       onListen: () {
         scheduleMicrotask(() {
-          JS('', '#(#, null)', helperCallback, async_error_codes.SUCCESS);
+          _wrapJsFunctionForAsync(body,

[floitsch, 2015/02/20 12:16:08]

nit: the "(null)" drowns.
maybe:
Function wrapped = _wrapJs...(
   body, async_error_codes.SUCCESS);
wrapped(null);

?

[sigurdm, 2015/02/23 12:33:49]

Done.

+                                  async_error_codes.SUCCESS)(null);
         });
       },
       onResume: () {
         if (!isAdding) {
-          asyncStarHelper(null, helperCallback, this);
+          asyncStarHelper(null, body, this);
         }
       }, onCancel: () {
         stopRunning = true;
       });
   }
 }
 
-makeAsyncStarController(helperCallback) {
-  return new AsyncStarStreamController(helperCallback);
+makeAsyncStarController(body) {
+  return new AsyncStarStreamController(body);
 }
 
 class IterationMarker {
   static const YIELD_SINGLE = 0;
   static const YIELD_STAR = 1;
   static const ITERATION_ENDED = 2;
   static const UNCAUGHT_ERROR = 3;
 
   final value;
   final int state;
@@ skipping 87 matching lines @@
   // This is a function that will return a helper function that does the
   // iteration of the sync*.
   //
   // Each invocation should give a body with fresh state.
   final dynamic /* js function */ _outerHelper;
 
   SyncStarIterable(this._outerHelper);
 
   Iterator get iterator => new SyncStarIterator(JS('', '#()', _outerHelper));
 }