Fix problem occurring when an async* stream is paused at the end of a yield*.

runtime/lib/async_patch.dart

 // Copyright (c) 2015, 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.
 
 import "dart:_internal";
 
 // We need to pass the value as first argument and leave the second and third
 // arguments empty (used for error handling).
 // See vm/ast_transformer.cc for usage.
 Function _asyncThenWrapperHelper(continuation) {
@@ skipping 106 matching lines @@
   bool addStream(Stream stream) {
     if (!onListenReceived) _fatal("yield before stream is listened to!");
     // If stream is cancelled, tell caller to exit the async generator.
     if (!controller.hasListener) return true;
     isAdding = true;
     var whenDoneAdding =
         controller.addStream(stream as Stream, cancelOnError: false);
     whenDoneAdding.then((_) {
       isAdding = false;
       scheduleGenerator();
+      if (!isScheduled) isSuspendedAtYield = true;
     });
     return false;
   }
 
   void addError(error, stackTrace) {
     if ((cancellationCompleter != null) && !cancellationCompleter.isCompleted) {
       // If the stream has been cancelled, complete the cancellation future
       // with the error.
       cancellationCompleter.completeError(error, stackTrace);
       return;
@@ skipping 45 matching lines @@
       // suspended at an await.
       if (isSuspendedAtYield) {
         scheduleGenerator();
       }
     }
     return cancellationCompleter.future;
   }
 }
 
 @patch void _rethrow(Object error, StackTrace stackTrace) native "Async_rethrow";