Remove a source of flakiness from async_step_test.

runtime/observatory/tests/service/async_step_test.dart

Index: runtime/observatory/tests/service/async_step_test.dart
diff --git a/runtime/observatory/tests/service/async_step_test.dart b/runtime/observatory/tests/service/async_step_test.dart
index 3ccbbe0ca8da28b5ea4af62dc38c988f93fed4cb..fb0fafd202770ccbc744e79be1aef1444d1812ce 100644
--- a/runtime/observatory/tests/service/async_step_test.dart
+++ b/runtime/observatory/tests/service/async_step_test.dart
@@ -25,11 +25,12 @@ testMain() {
   doAsync(true);
 }
 
-
 asyncStep(Isolate isolate) async {
-  var event = isolate.pauseEvent;
+  await isolate.reload(); // isolate.pauseEvent may be stale
+  ServiceEvent event = isolate.pauseEvent;
   print("Pause event is $event");
   expect(event, isNotNull);
+  expect(event.kind, equals(ServiceEvent.kPauseBreakpoint));
 
   // 1. Set breakpoint for the continuation and resume the isolate.
   Instance continuation = event.asyncContinuation;