Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/build/preserves_htaccess_test.dart

-// Copyright (c) 2013, 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 '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-
-  integration("preserves .htaccess as a special case", () {
-    d.dir(
-        appPath,
-        [
-            d.appPubspec(),
-            d.dir(
-                'web',
-                [d.file('.htaccess', 'fblthp'), d.file('.hidden', 'asdfgh')])]).create();
-
-    schedulePub(
-        args: ["build"],
-        output: new RegExp(r'Built \d+ files? to "build".'));
-
-    d.dir(
-        appPath,
-        [
-            d.dir(
-                'build',
-                [
-                    d.dir(
-                        'web',
-                        [d.file('.htaccess', 'fblthp'), d.nothing('.hidden')])])]).validate();
-  });
-}