Add support for listing to the glob package.

pkg/glob/lib/src/stream_pool.dart

Index: pkg/glob/lib/src/stream_pool.dart
diff --git a/pkg/barback/lib/src/utils/stream_pool.dart b/pkg/glob/lib/src/stream_pool.dart
similarity index 88%
copy from pkg/barback/lib/src/utils/stream_pool.dart
copy to pkg/glob/lib/src/stream_pool.dart
index 679672d2547e00db179138076efe7db2669345a2..641751333426d903d2f021515bd30a5fb6034225 100644
--- a/pkg/barback/lib/src/utils/stream_pool.dart
+++ b/pkg/glob/lib/src/stream_pool.dart
@@ -2,7 +2,7 @@
 // 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';
 
@@ -16,6 +16,9 @@ class StreamPool<T> {
   /// 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
@@ -53,6 +56,7 @@ class StreamPool<T> {
   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].
@@ -63,4 +67,10 @@ class StreamPool<T> {
     _subscriptions.clear();
     _controller.close();
   }
+
+  /// The next time this pool becomes empty, close it.
+  void closeWhenEmpty() {
+    if (_subscriptions.isEmpty) close();
+    _closeWhenEmpty = true;
+  }
 }