Don't double-complete in host.dart.

lib/src/runner/browser/static/host.dart.js

 // Generated by dart2js, the Dart to JavaScript compiler version: 1.10.0-edge.45075.
 // The code supports the following hooks:
 // dartPrint(message):
 //    if this function is defined it is called instead of the Dart [print]
 //    method.
 //
 // dartMainRunner(main, args):
 //    if this function is defined, the Dart [main] method will not be invoked
 //    directly. Instead, a closure that will invoke [main], and its arguments
 //    [args] is passed to [dartMainRunner].
@@ skipping 12754 matching lines @@
     if (t1 >= $length)
       return string;
     for (t1 = $length - string.length, t2 = string, i = 0; i < t1; ++i)
       t2 += " ";
     return t2.charCodeAt(0) == 0 ? t2 : t2;
   }
 }],
 ["test.multi_channel", "package:test/src/util/multi_channel.dart", , V, {
   "^": "",
   _MultiChannel: {
-    "^": "StreamChannelMixin;_innerStream,_innerSink,_innerStreamSubscription,_streamController,_sinkController,_streamControllers,_sinkControllers,_nextId",
+    "^": "StreamChannelMixin;_innerStream,_innerSink,_innerStreamSubscription,_closed,_streamController,_sinkController,_streamControllers,_sinkControllers,_nextId",
     virtualChannel$1: function(id) {
       var t1, t2, inputId, t3, streamController, sinkController;
       t1 = {};
       if (this._innerStream == null)
         throw H.wrapException(P.StateError$("The underlying channel is closed."));
       t1._captured_inputId_0 = null;
       t1._captured_outputId_1 = null;
       if (id != null) {
         t1._captured_inputId_0 = id;
         t1._captured_outputId_1 = H.intTypeCast(id) + 1;
@@ skipping 11 matching lines @@
         throw H.wrapException(P.ArgumentError$("A virtual channel with id " + H.S(id) + " already exists."));
       streamController = P.StreamController_StreamController(null, null, null, null, true, null);
       sinkController = P.StreamController_StreamController(null, null, null, null, true, null);
       t3.$indexSet(0, t1._captured_inputId_0, streamController);
       this._sinkControllers.$indexSet(0, t1._captured_inputId_0, sinkController);
       H.setRuntimeTypeInfo(new P._ControllerStream(sinkController), [null]).listen$2$onDone(new V._MultiChannel_virtualChannel_closure(t1, this), new V._MultiChannel_virtualChannel_closure0(t1, this));
       return new V.VirtualChannel(this, t1._captured_outputId_1, H.setRuntimeTypeInfo(new P._ControllerStream(streamController), [null]), H.setRuntimeTypeInfo(new P._StreamSinkWrapper(sinkController), [H.getRuntimeTypeArgument(sinkController, "_StreamController", 0)]));
     },
     _closeChannel$2: function(inputId, outputId) {
       var t1, t2;
+      if (this._closed)
+        return;
+      this._closed = true;
       t1 = this._streamControllers;
       J.close$0$x(t1.remove$1(0, inputId));
       J.close$0$x(this._sinkControllers.remove$1(0, inputId));
       t2 = this._innerSink;
       if (t2 == null)
         return;
       t2 = t2._async$_target;
       if (t2._state >= 4)
         H.throwExpression(t2._badEventState$0());
       t2._async$_add$1([outputId]);
@@ skipping 11 matching lines @@
     _MultiChannel$2: function(_innerStream, _innerSink) {
       var t1, t2;
       t1 = this._streamController;
       this._streamControllers.$indexSet(0, 0, t1);
       t2 = this._sinkController;
       this._sinkControllers.$indexSet(0, 0, t2);
       H.setRuntimeTypeInfo(new P._ControllerStream(t2), [null]).listen$2$onDone(new V._MultiChannel_closure(this), new V._MultiChannel_closure0(this));
       this._innerStreamSubscription = this._innerStream.listen$3$onDone$onError(new V._MultiChannel_closure1(this), this.get$_closeInnerChannel(), t1.get$addError());
     },
     static: {_MultiChannel$: function(_innerStream, _innerSink) {
-        var t1 = new V._MultiChannel(_innerStream, _innerSink, null, P.StreamController_StreamController(null, null, null, null, true, null), P.StreamController_StreamController(null, null, null, null, true, null), P.LinkedHashMap_LinkedHashMap(null, null, null, P.$int, P.StreamController), P.LinkedHashMap_LinkedHashMap(null, null, null, P.$int, P.StreamController), 1);
+        var t1 = new V._MultiChannel(_innerStream, _innerSink, null, false, P.StreamController_StreamController(null, null, null, null, true, null), P.StreamController_StreamController(null, null, null, null, true, null), P.LinkedHashMap_LinkedHashMap(null, null, null, P.$int, P.StreamController), P.LinkedHashMap_LinkedHashMap(null, null, null, P.$int, P.StreamController), 1);
         t1._MultiChannel$2(_innerStream, _innerSink);
         return t1;
       }}
   },
   _MultiChannel_closure: {
     "^": "Closure:2;_multi_channel$_captured_this_0",
     call$1: function(message) {
       var t1 = this._multi_channel$_captured_this_0._innerSink._async$_target;
       if (t1._state >= 4)
         H.throwExpression(t1._badEventState$0());
@@ skipping 135 matching lines @@
       if (t2 !== (t3 && C.Location_methods).get$origin(t3))
         return;
       if (!J.$eq(J.$index$asx(t1.get$data(message), "href"), J.get$src$x(this._captured_iframe_0)))
         return;
       message.stopPropagation();
       t1 = this._captured_inputController_1;
       t2 = J.$index$asx(P.convertNativeToDart_AcceptStructuredClone(message.data, true), "data");
       if (t1._state >= 4)
         H.throwExpression(t1._badEventState$0());
       t1._async$_add$1(t2);
-      this._captured_readyCompleter_2.complete$0(0);
+      t1 = this._captured_readyCompleter_2;
+      if (t1.future._state === 0)
+        t1.complete$0(0);
     }
   },
   _connectToIframe_closure0: {
     "^": "Closure:2;_captured_iframe_3,_captured_readyCompleter_4",
     call$1: function(message) {
       this._captured_readyCompleter_4.future.then$1(new R._connectToIframe__closure(this._captured_iframe_3, message));
     }
   },
   _connectToIframe__closure: {
     "^": "Closure:2;_captured_iframe_5,_captured_message_6",
@@ skipping 1016 matching lines @@
   else
     (function(a) {
       H.startRootIsolate(R.main$closure(), a);
     })([]);
 });
 ;
 // END invoke [main].
 })()
 
 //# sourceMappingURL=host.dart.js.map