Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/build/outputs_results_to_json_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:scheduled_test/scheduled_test.dart';
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-
-  integration("outputs results to JSON in a successful build", () {
-    // Dart2js can take a long time to compile dart code, so we increase the
-    // timeout to cope with that.
-    currentSchedule.timeout *= 3;
-
-    d.dir(
-        appPath,
-        [
-            d.appPubspec(),
-            d.dir(
-                'web',
-                [d.file('main.dart', 'void main() => print("hello");')])]).create();
-
-    schedulePub(args: ["build", "--format", "json"], outputJson: {
-      'buildResult': 'success',
-      'outputDirectory': 'build',
-      'numFiles': 1,
-      'log': [{
-          'level': 'Info',
-          'transformer': {
-            'name': 'Dart2JS',
-            'primaryInput': {
-              'package': 'myapp',
-              'path': 'web/main.dart'
-            }
-          },
-          'assetId': {
-            'package': 'myapp',
-            'path': 'web/main.dart'
-          },
-          'message': 'Compiling myapp|web/main.dart...'
-        }, {
-          'level': 'Info',
-          'transformer': {
-            'name': 'Dart2JS',
-            'primaryInput': {
-              'package': 'myapp',
-              'path': 'web/main.dart'
-            }
-          },
-          'assetId': {
-            'package': 'myapp',
-            'path': 'web/main.dart'
-          },
-          'message': contains(r'to compile myapp|web/main.dart.')
-        }, {
-          'level': 'Fine',
-          'transformer': {
-            'name': 'Dart2JS',
-            'primaryInput': {
-              'package': 'myapp',
-              'path': 'web/main.dart'
-            }
-          },
-          'assetId': {
-            'package': 'myapp',
-            'path': 'web/main.dart'
-          },
-          'message': contains(r'Took')
-        }]
-    });
-  });
-}