Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/upgrade/report/describes_change_test.dart

-// Copyright (c) 2013, 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("shows how package changed from previous lockfile", () {
-    servePackages((builder) {
-      builder.serve("unchanged", "1.0.0");
-      builder.serve("version_changed", "1.0.0");
-      builder.serve("version_changed", "2.0.0");
-      builder.serve("source_changed", "1.0.0");
-    });
-
-    d.dir(
-        "source_changed",
-        [d.libDir("source_changed"), d.libPubspec("source_changed", "2.0.0")]).create();
-
-    d.dir(
-        "description_changed_1",
-        [
-            d.libDir("description_changed"),
-            d.libPubspec("description_changed", "1.0.0")]).create();
-
-    d.dir(
-        "description_changed_2",
-        [
-            d.libDir("description_changed"),
-            d.libPubspec("description_changed", "1.0.0")]).create();
-
-    // Create the first lockfile.
-    d.appDir({
-      "unchanged": "any",
-      "version_changed": "1.0.0",
-      "source_changed": "any",
-      "description_changed": {
-        "path": "../description_changed_1"
-      }
-    }).create();
-
-    pubGet();
-
-    // Change the pubspec.
-    d.appDir({
-      "unchanged": "any",
-      "version_changed": "any",
-      "source_changed": {
-        "path": "../source_changed"
-      },
-      "description_changed": {
-        "path": "../description_changed_2"
-      }
-    }).create();
-
-    // Upgrade everything.
-    pubUpgrade(output: new RegExp(r"""
-Resolving dependencies\.\.\..*
-. description_changed 1\.0\.0 from path \.\.[/\\]description_changed_2 \(was 1\.0\.0 from path \.\.[/\\]description_changed_1\)
-. source_changed 2\.0\.0 from path \.\.[/\\]source_changed \(was 1\.0\.0\)
-. unchanged 1\.0\.0
-. version_changed 2\.0\.0 \(was 1\.0\.0\)
-""", multiLine: true));
-  });
-}