Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/cache/add/missing_package_arg_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.
-
-library pub_tests;
-
-import '../../../lib/src/exit_codes.dart' as exit_codes;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('fails if no package was given', () {
-    schedulePub(args: ["cache", "add"], error: """
-            No package to add given.
-            
-            Usage: pub cache add <package> [--version <constraint>] [--all]
-            -h, --help       Print this usage information.
-                --all        Install all matching versions.
-            -v, --version    Version constraint.
-
-            Run "pub help" to see global options.
-            See http://dartlang.org/tools/pub/cmd/pub-cache.html for detailed documentation.
-            """, exitCode: exit_codes.USAGE);
-  });
-}