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

sdk/lib/_internal/pub_generated/test/serve/native_watch_removed_file_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 'package:path/path.dart' as path;
-import 'package:scheduled_test/scheduled_test.dart';
-
-import '../../lib/src/io.dart';
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-import 'utils.dart';
-
-// TODO(nweiz): Default to testing the native watcher and add an explicit test
-// for the polling watcher when issue 14941 is fixed.
-
-main() {
-  initConfig();
-  integration(
-      "stop serving a file that is removed when using the native " "watcher",
-      () {
-    d.dir(
-        appPath,
-        [d.appPubspec(), d.dir("web", [d.file("index.html", "body")])]).create();
-
-    pubServe(args: ["--no-force-poll"]);
-    requestShouldSucceed("index.html", "body");
-
-    schedule(
-        () => deleteEntry(path.join(sandboxDir, appPath, "web", "index.html")));
-
-    waitForBuildSuccess();
-    requestShould404("index.html");
-    endPubServe();
-  });
-}