Modernize the package's style.

lib/src/future_group.dart

 // Copyright (c) 2015, 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 async.future_group;
-
 import 'dart:async';
 
 /// A collection of futures waits until all added [Future]s complete.
 ///
 /// Futures are added to the group with [add]. Once you're finished adding
 /// futures, signal that by calling [close]. Then, once all added futures have
 /// completed, [future] will complete with a list of values from the futures in
 /// the group, in the order they were added.
 ///
 /// If any added future completes with an error, [future] will emit that error
@@ skipping 11 matching lines @@
   var _closed = false;
 
   /// The future that fires once [close] has been called and all futures in the
   /// group have completed.
   ///
   /// This will also complete with an error if any of the futures in the group
   /// fails, regardless of whether [close] was called.
   Future<List<T>> get future => _completer.future;
   final _completer = new Completer<List<T>>();
 
-  /// Whether this group is waiting on any futures.
+  /// Returns `true` if this group isn't waiting on any futures.

[Lasse Reichstein Nielsen, 2016/03/08 10:40:37]

A getter is no different from a (final) field.
I'd prefer to document it like a filed, that is: as a property, not a function.
Returning is something that functions do - it's describing the *behavior* of the
function, not what it *is*.

[nweiz, 2016/03/08 20:23:39]

Done.

   bool get isIdle => _pending == 0;
 
   /// A broadcast stream that emits a `null` event whenever the last pending
   /// future in this group completes.
   ///
   /// Once this group isn't waiting on any futures *and* [close] has been
   /// called, this stream will close.
   Stream get onIdle {
     if (_onIdleController == null) {
       _onIdleController = new StreamController.broadcast(sync: true);
@@ skipping 40 matching lines @@
   /// Signals to the group that the caller is done adding futures, and so
   /// [future] should fire once all added futures have completed.
   void close() {
     _closed = true;
     if (_pending != 0) return;
     if (_completer.isCompleted) return;
     _completer.complete(_values);
   }
 }