Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/list_package_dirs/includes_dev_dependencies_test.dart

-// Copyright (c) 2013, 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 d.file.
-
-import 'package:path/path.dart' as path;
-
-import '../../lib/src/io.dart';
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('includes dev dependencies in the results', () {
-    d.dir("foo", [d.libDir("foo"), d.libPubspec("foo", "1.0.0")]).create();
-
-    d.dir(appPath, [d.pubspec({
-        "name": "myapp",
-        "dev_dependencies": {
-          "foo": {
-            "path": path.join(sandboxDir, "foo")
-          }
-        }
-      })]).create();
-
-    pubGet();
-
-    // Note: Using canonicalize here because pub gets the path to the
-    // entrypoint package from the working directory, which has had symlinks
-    // resolve. On Mac, "/tmp" is actually a symlink to "/private/tmp", so we
-    // need to accomodate that.
-    schedulePub(args: ["list-package-dirs", "--format=json"], outputJson: {
-      "packages": {
-        "foo": path.join(sandboxDir, "foo", "lib"),
-        "myapp": canonicalize(path.join(sandboxDir, appPath, "lib"))
-      },
-      "input_files": [
-          canonicalize(path.join(sandboxDir, appPath, "pubspec.lock")),
-          canonicalize(path.join(sandboxDir, appPath, "pubspec.yaml"))]
-    });
-  });
-}