Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/run/nonexistent_script_in_dependency_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 p;
-
-import '../../lib/src/exit_codes.dart' as exit_codes;
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('Errors if the script in a dependency does not exist.', () {
-    d.dir("foo", [d.libPubspec("foo", "1.0.0")]).create();
-
-    d.dir(appPath, [d.appPubspec({
-        "foo": {
-          "path": "../foo"
-        }
-      })]).create();
-
-    pubGet();
-
-    var pub = pubRun(args: ["foo:script"]);
-    pub.stderr.expect(
-        "Could not find ${p.join("bin", "script.dart")} in package foo.");
-    pub.shouldExit(exit_codes.NO_INPUT);
-  });
-}