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

sdk/lib/_internal/pub_generated/test/get/path/no_pubspec_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 d.file.
-
-import 'package:path/path.dart' as path;
-
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('path dependency to non-package directory', () {
-    // Make an empty directory.
-    d.dir('foo').create();
-    var fooPath = path.join(sandboxDir, "foo");
-
-    d.dir(appPath, [d.appPubspec({
-        "foo": {
-          "path": fooPath
-        }
-      })]).create();
-
-    pubGet(
-        error: new RegExp(
-            r'Could not find a file named "pubspec.yaml" ' r'in "[^\n]*"\.'));
-  });
-}