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

sdk/lib/_internal/pub_generated/lib/src/barback/excluding_transformer.dart

Index: sdk/lib/_internal/pub_generated/lib/src/barback/excluding_transformer.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/barback/excluding_transformer.dart b/sdk/lib/_internal/pub_generated/lib/src/barback/excluding_transformer.dart
deleted file mode 100644
index 52d90a991d2d9760ee5115fe4c248c2bd9ac02e5..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/lib/src/barback/excluding_transformer.dart
+++ /dev/null
@@ -1,67 +0,0 @@
-// 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.
-
-library pub.excluding_transformer;
-
-import 'dart:async';
-
-import 'package:barback/barback.dart';
-
-import 'transformer_config.dart';
-
-/// Decorates an inner [Transformer] and handles including and excluding
-/// primary inputs.
-class ExcludingTransformer extends Transformer {
-  /// If [config] defines includes or excludes, wraps [inner] in an
-  /// [ExcludingTransformer] that handles those.
-  ///
-  /// Otherwise, just returns [inner] unmodified.
-  static Transformer wrap(Transformer inner, TransformerConfig config) {
-    if (!config.hasExclusions) return inner;
-
-    if (inner is LazyTransformer) {
-      // TODO(nweiz): Remove these unnecessary "as"es when issue 19046 is fixed.
-      return new _LazyExcludingTransformer(inner as LazyTransformer, config);
-    } else if (inner is DeclaringTransformer) {
-      return new _DeclaringExcludingTransformer(
-          inner as DeclaringTransformer,
-          config);
-    } else {
-      return new ExcludingTransformer._(inner, config);
-    }
-  }
-
-  final Transformer _inner;
-
-  /// The config containing rules for which assets to include or exclude.
-  final TransformerConfig _config;
-
-  ExcludingTransformer._(this._inner, this._config);
-
-  isPrimary(AssetId id) {
-    if (!_config.canTransform(id.path)) return false;
-    return _inner.isPrimary(id);
-  }
-
-  Future apply(Transform transform) => _inner.apply(transform);
-
-  String toString() => _inner.toString();
-}
-
-class _DeclaringExcludingTransformer extends ExcludingTransformer implements
-    DeclaringTransformer {
-  _DeclaringExcludingTransformer(DeclaringTransformer inner,
-      TransformerConfig config)
-      : super._(inner as Transformer, config);
-
-  Future declareOutputs(DeclaringTransform transform) =>
-      (_inner as DeclaringTransformer).declareOutputs(transform);
-}
-
-class _LazyExcludingTransformer extends _DeclaringExcludingTransformer
-    implements LazyTransformer {
-  _LazyExcludingTransformer(DeclaringTransformer inner,
-      TransformerConfig config)
-      : super(inner, config);
-}