Make use of Completer.isComplete in pub and pkg/scheduled_test.

pkg/scheduled_test/test/utils.dart

Index: pkg/scheduled_test/test/utils.dart
diff --git a/pkg/scheduled_test/test/utils.dart b/pkg/scheduled_test/test/utils.dart
index 42f5c22a9b1ae84010da2af1451a37460d822996..3d59e660b81a919beef9eb52700975860a46eedc 100644
--- a/pkg/scheduled_test/test/utils.dart
+++ b/pkg/scheduled_test/test/utils.dart
@@ -20,19 +20,16 @@ export 'package:scheduled_test/src/utils.dart';
 /// Note that timing out will not cancel the asynchronous operation behind
 /// [input].
 Future timeout(Future input, int milliseconds, onTimeout()) {
-  bool completed = false;
   var completer = new Completer();
   var timer = new Timer(new Duration(milliseconds: milliseconds), () {
-    completed = true;
-    chainToCompleter(new Future.immediate(null).then((_) => onTimeout()),
-        completer);
+    chainToCompleter(new Future.of(onTimeout), completer);
   });
   input.then((value) {
-    if (completed) return;
+    if (completer.isCompleted) return;
     timer.cancel();
     completer.complete(value);
   }).catchError((e) {
-    if (completed) return;
+    if (completer.isCompleted) return;
     timer.cancel();
     completer.completeError(e.error, e.stackTrace);
   });