Fix tests that don't catch asynchronous errors from isolate spawning. Update co19 status.

tests/isolate/message_enum_test.dart

Index: tests/isolate/message_enum_test.dart
diff --git a/tests/isolate/message_enum_test.dart b/tests/isolate/message_enum_test.dart
index 7dbaec3bb9964017296209cc9450a847925c601a..b06dfc34259d118494597a24f537c1416e3f9866 100644
--- a/tests/isolate/message_enum_test.dart
+++ b/tests/isolate/message_enum_test.dart
@@ -5,6 +5,7 @@
 // SharedOptions=--enable-enum
 
 import 'package:expect/expect.dart';
+import 'package:async_helper/async_helper.dart';
 import "dart:isolate";
 
 enum Foo { BAR, BAZ }
@@ -18,7 +19,8 @@ main() {
     Expect.equals(42, map[key]);
     p.close();
   });
-  Isolate.spawn(sendIt, p.sendPort);
+  asyncStart();
+  Isolate.spawn(sendIt, p.sendPort).whenComplete(asyncEnd);
 }
 
 void sendIt(port) {