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

sdk/lib/_internal/pub_generated/test/run/runs_app_in_directory_in_entrypoint_test.dart

-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS 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.
-
-import 'package:path/path.dart' as path;
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('runs a Dart application in the entrypoint package', () {
-    d.dir(
-        appPath,
-        [
-            d.appPubspec(),
-            d.dir(
-                "tool",
-                [
-                    d.file("app.dart", "main() => print('tool');"),
-                    d.dir("sub", [d.file("app.dart", "main() => print('sub');")])])]).create();
-
-    var pub = pubRun(args: [path.join("tool", "app")]);
-    pub.stdout.expect("tool");
-    pub.shouldExit();
-
-    pub = pubRun(args: [path.join("tool", "sub", "app")]);
-    pub.stdout.expect("sub");
-    pub.shouldExit();
-  });
-}