Fix pub errorgroup and analyzer errors.

tests/lib/async/stream_state_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 stream_state_helper;
 
 import "../../../pkg/unittest/lib/unittest.dart";
 import "dart:async";
 import "dart:collection";
 
@@ skipping 501 matching lines @@
   bool _testSubscribe() => true;
   String toString() => "[Subscribed]";
 }
 
 class CancelCallbackEvent extends Event {
   CancelCallbackEvent(void action()) : super(action);
   bool _testCancel() => true;
   String toString() => "[Cancelled]";
 }
 
-class _BroadcastEventCallback extends Event {
-  Function _action;
-  _BroadcastEventCallback();
-}
-
 class BroadcastCancelCallbackEvent extends Event {
   BroadcastCancelCallbackEvent(void action(StreamSubscription sub))
     : super.broadcast(action);
   bool _testBroadcastCancel() => true;
   String toString() => "[BroadcastCancel]";
 }
 
 class BroadcastListenCallbackEvent extends Event {
   BroadcastListenCallbackEvent(void action(StreamSubscription sub))
     : super.broadcast(action);
@@ skipping 48 matching lines @@
   }
 
   bool _testBroadcastCancel() {
     _actual = "*[BroadcastCancel]";
     return true;
   }
 
   /** Returns a representation of the event it was tested against. */
   String toString() => _actual;
 }