Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/barback/fails_if_dir_arg_does_not_exist_test.dart

Index: sdk/lib/_internal/pub_generated/test/barback/fails_if_dir_arg_does_not_exist_test.dart
diff --git a/sdk/lib/_internal/pub_generated/test/barback/fails_if_dir_arg_does_not_exist_test.dart b/sdk/lib/_internal/pub_generated/test/barback/fails_if_dir_arg_does_not_exist_test.dart
deleted file mode 100644
index 3e31c5acd8de0ddf4505c96156c98a920ca361e1..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/test/barback/fails_if_dir_arg_does_not_exist_test.dart
+++ /dev/null
@@ -1,26 +0,0 @@
-// Copyright (c) 2014, 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.
-
-import 'package:scheduled_test/scheduled_test.dart';
-
-import '../../lib/src/exit_codes.dart' as exit_codes;
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-import 'utils.dart';
-
-main() {
-  initConfig();
-
-  setUp(() {
-    d.dir(
-        appPath,
-        [d.appPubspec(), d.dir("bar", [d.file("file.txt", "contents")])]).create();
-  });
-
-  pubBuildAndServeShouldFail(
-      "if a specified directory doesn't exist",
-      args: ["foo", "bar", "baz"],
-      error: 'Directories "foo" and "baz" do not exist.',
-      exitCode: exit_codes.DATA);
-}