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

sdk/lib/_internal/pub_generated/lib/src/validator/directory.dart

Index: sdk/lib/_internal/pub_generated/lib/src/validator/directory.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/validator/directory.dart b/sdk/lib/_internal/pub_generated/lib/src/validator/directory.dart
deleted file mode 100644
index a9935e8461d922d33c43ad0555a33b26d5ea9033..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/lib/src/validator/directory.dart
+++ /dev/null
@@ -1,51 +0,0 @@
-// 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.validator.directory;
-
-import 'dart:async';
-
-import 'package:path/path.dart' as path;
-
-import '../entrypoint.dart';
-import '../io.dart';
-import '../validator.dart';
-
-/// A validator that validates a package's top-level directories.
-class DirectoryValidator extends Validator {
-  DirectoryValidator(Entrypoint entrypoint)
-      : super(entrypoint);
-
-  static final _PLURAL_NAMES = [
-      "benchmarks",
-      "docs",
-      "examples",
-      "tests",
-      "tools"];
-
-  Future validate() {
-    return new Future.sync(() {
-      for (var dir in listDir(entrypoint.root.dir)) {
-        if (!dirExists(dir)) continue;
-
-        dir = path.basename(dir);
-        if (_PLURAL_NAMES.contains(dir)) {
-          // Cut off the "s"
-          var singularName = dir.substring(0, dir.length - 1);
-          warnings.add(
-              'Rename the top-level "$dir" directory to ' '"$singularName".\n'
-                  'The Pub layout convention is to use singular directory ' 'names.\n'
-                  'Plural names won\'t be correctly identified by Pub and other ' 'tools.');
-        }
-
-        if (dir.contains(new RegExp(r"^samples?$"))) {
-          warnings.add(
-              'Rename the top-level "$dir" directory to "example".\n'
-                  'This allows Pub to find your examples and create "packages" '
-                  'directories for them.\n');
-        }
-      }
-    });
-  }
-}