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

sdk/lib/_internal/pub_generated/test/downgrade/dry_run_does_not_apply_changes_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.
 
 import 'package:path/path.dart' as path;
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../lib/src/io.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
@@ skipping 17 matching lines @@
     d.appDir({
       "foo": "any"
     }).create();
 
     // Also delete the "packages" directory.
     schedule(() {
       deleteEntry(path.join(sandboxDir, appPath, "packages"));
     });
 
     // Do the dry run.
-    pubDowngrade(args: ["--dry-run"], output: allOf([
-      contains("< foo 1.0.0"),
-      contains("Would change 1 dependency.")
-    ]));
+    pubDowngrade(
+        args: ["--dry-run"],
+        output: allOf(
+            [contains("< foo 1.0.0"), contains("Would change 1 dependency.")]));
 
-    d.dir(appPath, [
-      // The lockfile should be unmodified.
+    d.dir(appPath, [// The lockfile should be unmodified.
       d.matcherFile("pubspec.lock", contains("2.0.0")),
-      // The "packages" directory should not have been regenerated.
-      d.nothing("packages")
-    ]).validate();
+          // The "packages" directory should not have been regenerated.
+      d.nothing("packages")]).validate();
   });
 }