Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/hosted/version_negotiation_test.dart

-// Copyright (c) 2012, 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_server.dart';
-import 'package:scheduled_test/scheduled_test.dart';
-import 'package:shelf/shelf.dart' as shelf;
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-
-  forBothPubGetAndUpgrade((command) {
-    integration('sends the correct Accept header', () {
-      var server = new ScheduledServer();
-
-      d.appDir({
-        "foo": {
-          "hosted": {
-            "name": "foo",
-            "url": server.url.then((url) => url.toString())
-          }
-        }
-      }).create();
-
-      var pub = startPub(args: [command.name]);
-
-      server.handle('GET', '/api/packages/foo', (request) {
-        expect(
-            request.headers['accept'],
-            equals('application/vnd.pub.v2+json'));
-        return new shelf.Response(200);
-      });
-
-      pub.kill();
-    });
-
-    integration('prints a friendly error if the version is out-of-date', () {
-      var server = new ScheduledServer();
-
-      d.appDir({
-        "foo": {
-          "hosted": {
-            "name": "foo",
-            "url": server.url.then((url) => url.toString())
-          }
-        }
-      }).create();
-
-      var pub = startPub(args: [command.name]);
-
-      server.handle(
-          'GET',
-          '/api/packages/foo',
-          (request) => new shelf.Response(406));
-
-      pub.shouldExit(1);
-
-      pub.stderr.expect(
-          emitsLines(
-              "Pub 0.1.2+3 is incompatible with the current version of localhost.\n"
-                  "Upgrade pub to the latest version and try again."));
-    });
-  });
-}