Fix flaky async test.

tests/lib/async/stream_periodic3_test.dart

Index: tests/lib/async/stream_periodic3_test.dart
diff --git a/tests/lib/async/stream_periodic3_test.dart b/tests/lib/async/stream_periodic3_test.dart
index 437a8a685fe95d20fd65664804aa4bbe6030f918..b25ae2739fa513e0cf592381d721d489544db2b1 100644
--- a/tests/lib/async/stream_periodic3_test.dart
+++ b/tests/lib/async/stream_periodic3_test.dart
@@ -21,7 +21,7 @@ main() {
                                         (x) => x);
     stream.take(10).listen((_) { }, onDone: expectAsync(() {
       int millis = watch.elapsedMilliseconds + safetyMargin;
-      expect(millis, greaterThan(10));
+      expect(millis, greaterThanOrEqualTo(10));
     }));
   });
 }