Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/global/run/implicit_executable_name_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 '../../../lib/src/exit_codes.dart' as exit_codes;
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('defaults to the package name if the script is omitted', () {
-    servePackages((builder) {
-      builder.serve(
-          "foo",
-          "1.0.0",
-          contents: [d.dir("bin", [d.file("foo.dart", "main(args) => print('foo');")])]);
-    });
-
-    schedulePub(args: ["global", "activate", "foo"]);
-
-    var pub = pubRun(global: true, args: ["foo"]);
-    pub.stdout.expect("foo");
-    pub.shouldExit();
-  });
-}