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

sdk/lib/_internal/pub_generated/test/get/hosted/stay_locked_if_compatible_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 '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration(
-      "doesn't upgrade a locked pub server package with a new "
-          "compatible constraint",
-      () {
-    servePackages((builder) => builder.serve("foo", "1.0.0"));
-
-    d.appDir({
-      "foo": "any"
-    }).create();
-
-    pubGet();
-
-    d.packagesDir({
-      "foo": "1.0.0"
-    }).validate();
-
-    servePackages((builder) => builder.serve("foo", "1.0.1"));
-
-    d.appDir({
-      "foo": ">=1.0.0"
-    }).create();
-
-    pubGet();
-
-    d.packagesDir({
-      "foo": "1.0.0"
-    }).validate();
-  });
-}