Add StreamController.multiplex constructor.

pkg/scheduled_test/lib/src/mock_clock.dart

Index: pkg/scheduled_test/lib/src/mock_clock.dart
diff --git a/pkg/scheduled_test/lib/src/mock_clock.dart b/pkg/scheduled_test/lib/src/mock_clock.dart
index c80a9552661329cf8e4402afdb4bddf75652d473..46a37afcf2e246453071150d5b44fac314843f67 100644
--- a/pkg/scheduled_test/lib/src/mock_clock.dart
+++ b/pkg/scheduled_test/lib/src/mock_clock.dart
@@ -44,27 +44,14 @@ class Clock {
   int get time => _time;
   int _time = 0;
 
-  /// Collection of controllers of all subscribed listeners.
-  ///
-  /// [StreamController] is not overriding [Object.operator==], so this is
-  /// effectively an identity map.
-  Set<StreamController> _subscriptions = new Set<StreamController>();
+  /// Controller providing streams for listening.
+  StreamController<int> _multiplexController =
+      new StreamController<int>.multiplex();
 
   Clock._();
 
   /// The stream of millisecond ticks of the clock.
-  Stream<int> get onTick {
-    StreamController<int> controller;
-    controller = new StreamController<int>(
-        onListen: () {
-          _subscriptions.add(controller);
-        },
-        onCancel: () {
-          _subscriptions.remove(controller);
-        });
-    return controller.stream;
-  }
-
+  Stream<int> get onTick => _multiplexController.stream;
 
   /// Advances the clock forward by [milliseconds]. This works like synchronous
   /// code that takes [milliseconds] to execute; any [Timer]s that are scheduled
@@ -74,12 +61,7 @@ class Clock {
     for (var i = 0; i < milliseconds; i++) {
       var tickTime = ++_time;
       runAsync(() {
-        List<StreamController> controllers = _subscriptions.toList();
-        for (StreamController controller in controllers) {
-          if (_subscriptions.contains(controller)) {
-            controller.add(tickTime);
-          }
-        }
+        _multiplexController.add(tickTime);
       });
     }
   }
@@ -90,7 +72,7 @@ class Clock {
   /// code runs before the next tick.
   void run() {
     pumpEventQueue().then((_) {
-      if (_subscriptions.isEmpty) return;
+      if (!_multiplexController.hasListener) return;
       tick();
       return run();
     });