Revert "Use native async/await support in pub."

sdk/lib/_internal/pub_generated/test/serve/missing_asset_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library pub_tests;
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';
 
 main() {
   initConfig();
   integration("responds with a 404 for missing assets", () {
-    d.dir(appPath, [
-      d.appPubspec()
-    ]).create();
+    d.dir(appPath, [d.appPubspec()]).create();
 
     pubServe();
     requestShould404("index.html");
     requestShould404("packages/myapp/nope.dart");
     requestShould404("dir/packages/myapp/nope.dart");
     endPubServe();
   });
 }