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

sdk/lib/_internal/pub_generated/test/serve/gets_first_if_git_ref_changed_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 file.
-
-library pub_tests;
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-import 'utils.dart';
-
-main() {
-  initConfig();
-  integration(
-      "gets first if a git dependency's ref doesn't match the one in "
-          "the lock file",
-      () {
-    var repo =
-        d.git('foo.git', [d.libDir('foo', 'before'), d.libPubspec('foo', '1.0.0')]);
-    repo.create();
-    var commit1 = repo.revParse('HEAD');
-
-    d.git(
-        'foo.git',
-        [d.libDir('foo', 'after'), d.libPubspec('foo', '1.0.0')]).commit();
-
-    var commit2 = repo.revParse('HEAD');
-
-    // Lock it to the ref of the first commit.
-    d.appDir({
-      "foo": {
-        "git": {
-          "url": "../foo.git",
-          "ref": commit1
-        }
-      }
-    }).create();
-
-    pubGet();
-
-    // Change the commit in the pubspec.
-    d.appDir({
-      "foo": {
-        "git": {
-          "url": "../foo.git",
-          "ref": commit2
-        }
-      }
-    }).create();
-
-    pubServe(shouldGetFirst: true);
-    requestShouldSucceed("packages/foo/foo.dart", 'main() => "after";');
-    endPubServe();
-  });
-}