mpre fix

com.unity.uiwidgets/Runtime/async/broadcast_stream_controller.cs

             get { return new _StreamSinkWrapper<T>(this); }
         }
 
-        bool isClosed {
+        public override bool isClosed {
             get { return (_state & _STATE_CLOSED) != 0; }
         }
 
    * Each receiving stream may be paused individually, and they handle their
    * own buffering.
    */
-        bool isPaused {
+        public override bool isPaused {
-        bool hasListener {
+        public override bool hasListener {
             get => !_isEmpty;
         }
 

com.unity.uiwidgets/Runtime/async/stream_controller.cs

 
         public virtual StreamSink<T> sink { get; }
 
-        public bool isClosed { get; }
+        public virtual bool isClosed { get; }
-        public bool isPaused { get; }
+        public virtual bool isPaused { get; }
-        public bool hasListener { get; }
+        public virtual bool hasListener { get; }
 
         // public abstract void add(T evt);
         //
         }
 
         /** Whether there is an active listener. */
-        bool hasListener {
+        public override bool hasListener {
             get => (_state & _STATE_SUBSCRIBED) != 0;
         }
 
 //
     abstract class _SyncStreamControllerDispatch<T>
         : _StreamController<T>, SynchronousStreamController<T> {
-        int _state { get; set; }
+        internal virtual int _state { get; set; }
 
         public override void _sendData(T data) {
             _subscription._add(data);
             this._controller = _controller;
         }
 
-        StreamSubscription<T> _createSubscription(
+        internal override StreamSubscription<T> _createSubscription(
             Action<T> onData, Action<object, string> onError, Action onDone, bool cancelOnError) =>
             _controller._subscribe(onData, onError, onDone, cancelOnError);
 

com.unity.uiwidgets/Runtime/async/stream_impl.cs

 
         // -------------------------------------------------------------------
         /** Create a subscription object. Called by [subcribe]. */
-        StreamSubscription<T> _createSubscription(
+        internal virtual StreamSubscription<T> _createSubscription(
             Action<T> onData, Action<object, string> onError, Action onDone, bool cancelOnError) {
             return new _BufferingStreamSubscription<T>(
                 onData, onError, onDone, cancelOnError);
             this._pending = _pending;
         }
 
-        StreamSubscription<T> _createSubscription(
+        internal override StreamSubscription<T> _createSubscription(
             Action<T> onData, Action<object, string> onError, Action onDone, bool cancelOnError) {
             if (_isUsed) throw new Exception("Stream has already been listened to.");
             _isUsed = true;