Revert "Revert "Use native async/await support in pub.""

sdk/lib/_internal/pub_generated/test/run/mode_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 '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-const TRANSFORMER = """
-import 'dart:async';
-
-import 'package:barback/barback.dart';
-
-class DartTransformer extends Transformer {
-  final BarbackSettings _settings;
-
-  DartTransformer.asPlugin(this._settings);
-
-  String get allowedExtensions => '.in';
-
-  void apply(Transform transform) {
-    transform.addOutput(new Asset.fromString(
-        new AssetId(transform.primaryInput.id.package, "bin/script.dart"),
-        "void main() => print('\${_settings.mode.name}');"));
-  }
-}
-""";
-
-main() {
-  initConfig();
-  withBarbackVersions("any", () {
-    integration('runs a local script with customizable modes', () {
-      d.dir(appPath, [d.pubspec({
-          "name": "myapp",
-          "transformers": ["myapp/src/transformer"]
-        }),
-            d.dir(
-                "lib",
-                [
-                    d.dir(
-                        "src",
-                        [
-                            d.file("transformer.dart", TRANSFORMER),
-                            d.file("primary.in", "")])])]).create();
-
-      createLockFile('myapp', pkg: ['barback']);
-
-      // By default it should run in debug mode.
-      var pub = pubRun(args: ["script"]);
-      pub.stdout.expect("debug");
-      pub.shouldExit();
-
-      // A custom mode should be specifiable.
-      pub = pubRun(args: ["--mode", "custom-mode", "script"]);
-      pub.stdout.expect("custom-mode");
-      pub.shouldExit();
-    });
-
-    integration('runs a dependency script with customizable modes', () {
-      d.dir("foo", [d.pubspec({
-          "name": "foo",
-          "version": "1.2.3",
-          "transformers": ["foo/src/transformer"]
-        }),
-            d.dir(
-                "lib",
-                [
-                    d.dir(
-                        "src",
-                        [
-                            d.file("transformer.dart", TRANSFORMER),
-                            d.file("primary.in", "")])])]).create();
-
-      d.appDir({
-        "foo": {
-          "path": "../foo"
-        }
-      }).create();
-
-      createLockFile('myapp', sandbox: ['foo'], pkg: ['barback']);
-
-      // By default it should run in release mode.
-      var pub = pubRun(args: ["foo:script"]);
-      pub.stdout.expect("release");
-      pub.shouldExit();
-
-      // A custom mode should be specifiable.
-      pub = pubRun(args: ["--mode", "custom-mode", "foo:script"]);
-      pub.stdout.expect("custom-mode");
-      pub.shouldExit();
-    });
-  });
-}