Make pkg/stack_trace use stack chains.

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 9bfc913433a3a7270c3269abb12102f07bdf7ab8..6fc24f341557821ead32f1438ddf373c11a6206a 100644
--- a/pkg/scheduled_test/test/utils.dart
+++ b/pkg/scheduled_test/test/utils.dart
@@ -25,7 +25,7 @@ export 'package:scheduled_test/src/utils.dart';
 Future timeout(Future input, int milliseconds, onTimeout()) {
   var completer = new Completer();
   var timer = new Timer(new Duration(milliseconds: milliseconds), () {
-    chainToCompleter(new Future.sync(onTimeout), completer);
+    chainToCompleter(syncFuture(onTimeout), completer);
   });
   input.then((value) {
     if (completer.isCompleted) return;