Add test for whether a completer or stream controller has been closed.

sdk/lib/async/stream_controller.dart

 // Copyright (c) 2012, 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.
 
 part of dart.async;
 
 // -------------------------------------------------------------------
 // Controller for creating and adding events to a stream.
 // -------------------------------------------------------------------
 
@@ skipping 45 matching lines @@
   StreamController({void onPauseStateChange(),
                     void onSubscriptionStateChange()})
       : stream = new _SingleControllerStream<T>(onSubscriptionStateChange,
                                                 onPauseStateChange);
 
   /**
    * Returns a view of this object that only exposes the [StreamSink] interface.
    */
   StreamSink<T> get sink => new StreamSinkView<T>(this);
 
+  /**
+   * Whether the stream is closed for adding more events.
+   *
+   * If true, the "done" event might not have fired yet, but it has been
+   * scheduled, and it is too late to add more events.
+   */
+  bool get isClosed => stream._isClosed;
+
   /** Whether one or more active subscribers have requested a pause. */
   bool get isPaused => stream._isPaused;
 
   /** Whether there are currently any subscribers on this [Stream]. */
   bool get hasSubscribers => stream._hasSubscribers;
 
   /**
    * Send or queue a data event.
    */
   void add(T value) => stream._add(value);
@@ skipping 53 matching lines @@
   _SingleControllerStream(this._subscriptionHandler, this._pauseHandler);
 
   void _onSubscriptionStateChange() {
     if (_subscriptionHandler != null) _subscriptionHandler();
   }
 
   void _onPauseStateChange() {
     if (_pauseHandler != null) _pauseHandler();
   }
 }