Dart: Better handle leak checks. close() is async.

services/dart/dart_apptests/main.dart

Index: services/dart/dart_apptests/main.dart
diff --git a/services/dart/dart_apptests/main.dart b/services/dart/dart_apptests/main.dart
index c193530499aaa1191d82f2541cdbd053ab04ab94..54e1cc9228dddebbcf1236d6dd19c697e4ece3a5 100644
--- a/services/dart/dart_apptests/main.dart
+++ b/services/dart/dart_apptests/main.dart
@@ -5,9 +5,9 @@
 import 'package:apptest/apptest.dart';
 import 'package:services/dart/test/echo_service.mojom.dart';
 
-import 'echo_apptests.dart';
-import 'pingpong_apptests.dart';
+import 'echo_apptests.dart' as echo;
+import 'pingpong_apptests.dart' as pingpong;
 
 main(List args) {
-  runAppTests(args[0], [echoApptests, pingpongApptests]);
+  runAppTests(args[0], [echo.echoApptests, pingpong.pingpongApptests]);
 }