Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/dependency_computer/error_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 'package:scheduled_test/scheduled_test.dart';
-
-import '../../lib/src/exceptions.dart';
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-import 'utils.dart';
-
-void main() {
-  initConfig();
-
-  integration("fails if an unknown package is imported", () {
-    d.dir(appPath, [d.pubspec({
-        "name": "myapp",
-        "transformers": ["myapp"]
-      }),
-          d.dir(
-              'lib',
-              [d.file("myapp.dart", transformer(["package:foo/foo.dart"]))])]).create();
-
-    expectException(predicate((error) {
-      expect(error, new isInstanceOf<ApplicationException>());
-      expect(
-          error.message,
-          equals(
-              'A transformer imported unknown package "foo" (in '
-                  '"package:foo/foo.dart").'));
-      return true;
-    }));
-  });
-
-  integration("fails on a syntax error", () {
-    d.dir(appPath, [d.pubspec({
-        "name": "myapp",
-        "transformers": ["myapp"]
-      }), d.dir('lib', [d.file("myapp.dart", "library;")])]).create();
-
-    expectException(new isInstanceOf<AnalyzerErrorGroup>());
-  });
-}