Ensure that errors have stack traces attached.

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 88c0fa386bdb8f92d6af478087fa26d6819a53ea..9bfc913433a3a7270c3269abb12102f07bdf7ab8 100644
--- a/pkg/scheduled_test/test/utils.dart
+++ b/pkg/scheduled_test/test/utils.dart
@@ -31,10 +31,10 @@ Future timeout(Future input, int milliseconds, onTimeout()) {
     if (completer.isCompleted) return;
     timer.cancel();
     completer.complete(value);
-  }).catchError((error) {
+  }).catchError((error, stackTrace) {
     if (completer.isCompleted) return;
     timer.cancel();
-    completer.completeError(error);
+    completer.completeError(error, stackTrace);
   });
   return completer.future;
 }