Add support for listing to the glob package.

pkg/glob/lib/src/stream_pool.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 barback.utils.stream_pool;
+library glob.stream_pool;
 
 import 'dart:async';
 
 /// A pool of streams whose events are unified and emitted through a central
 /// stream.
 class StreamPool<T> {
   /// The stream through which all events from streams in the pool are emitted.
   Stream<T> get stream => _controller.stream;
   final StreamController<T> _controller;
 
   /// Subscriptions to the streams that make up the pool.
   final _subscriptions = new Map<Stream<T>, StreamSubscription<T>>();
 
+  /// Whether this pool should be closed when it becomes empty.
+  bool _closeWhenEmpty = false;
+
   /// Creates a new stream pool that only supports a single subscriber.
   ///
   /// Any events from broadcast streams in the pool will be buffered until a
   /// listener is subscribed.
   StreamPool()
       // Create the controller as sync so that any sync input streams will be
       // forwarded synchronously. Async input streams will have their asynchrony
       // preserved, since _controller.add will be called asynchronously.
       : _controller = new StreamController<T>(sync: true);
 
@@ skipping 17 matching lines @@
     if (_subscriptions.containsKey(stream)) return;
     _subscriptions[stream] = stream.listen(_controller.add,
         onError: _controller.addError,
         onDone: () => remove(stream));
   }
 
   /// Removes [stream] as a member of this pool.
   void remove(Stream<T> stream) {
     var subscription = _subscriptions.remove(stream);
     if (subscription != null) subscription.cancel();
+    if (_closeWhenEmpty && _subscriptions.isEmpty) close();
   }
 
   /// Removes all streams from this pool and closes [stream].
   void close() {
     for (var subscription in _subscriptions.values) {
       subscription.cancel();
     }
     _subscriptions.clear();
     _controller.close();
   }
+
+  /// The next time this pool becomes empty, close it.
+  void closeWhenEmpty() {
+    if (_subscriptions.isEmpty) close();
+    _closeWhenEmpty = true;
+  }
 }