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

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

Index: sdk/lib/_internal/pub_generated/lib/src/barback/transformer_id.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/barback/transformer_id.dart b/sdk/lib/_internal/pub_generated/lib/src/barback/transformer_id.dart
deleted file mode 100644
index 2017d9bb0a8cd6305545b51cc37836e8dfb880a9..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/lib/src/barback/transformer_id.dart
+++ /dev/null
@@ -1,99 +0,0 @@
-// 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.barback.transformer_id;
-
-import 'dart:async';
-
-import 'package:barback/barback.dart';
-import 'package:source_span/source_span.dart';
-
-import '../utils.dart';
-
-/// A list of the names of all built-in transformers that pub exposes.
-const _BUILT_IN_TRANSFORMERS = const ['\$dart2js'];
-
-/// An identifier that indicates the library that contains a transformer.
-///
-/// It's possible that the library identified by [this] defines multiple
-/// transformers. If so, they're all always loaded in the same phase.
-class TransformerId {
-  /// The package containing the library where the transformer is defined.
-  final String package;
-
-  /// The `/`-separated path to the library that contains this transformer.
-  ///
-  /// This is relative to the `lib/` directory in [package], and doesn't end in
-  /// `.dart`.
-  ///
-  /// This can be null; if so, it indicates that the transformer(s) should be
-  /// loaded from `lib/transformer.dart` if that exists, and `lib/$package.dart`
-  /// otherwise.
-  final String path;
-
-  /// The source span from which this id was parsed.
-  final SourceSpan span;
-
-  /// Whether this ID points to a built-in transformer exposed by pub.
-  bool get isBuiltInTransformer => package.startsWith('\$');
-
-  /// Parses a transformer identifier.
-  ///
-  /// A transformer identifier is a string of the form "package_name" or
-  /// "package_name/path/to/library". It does not have a trailing extension. If
-  /// it just has a package name, it expands to lib/transformer.dart if that
-  /// exists, or lib/${package}.dart otherwise. Otherwise, it expands to
-  /// lib/${path}.dart. In either case it's located in the given package.
-  factory TransformerId.parse(String identifier, SourceSpan span) {
-    if (identifier.isEmpty) {
-      throw new FormatException('Invalid library identifier: "".');
-    }
-
-    var parts = split1(identifier, "/");
-    if (parts.length == 1) {
-      return new TransformerId(parts.single, null, span);
-    }
-
-    return new TransformerId(parts.first, parts.last, span);
-  }
-
-  TransformerId(this.package, this.path, this.span) {
-    if (!package.startsWith('\$')) return;
-    if (_BUILT_IN_TRANSFORMERS.contains(package)) return;
-    throw new SourceSpanFormatException(
-        'Unsupported built-in transformer $package.',
-        span);
-  }
-
-  bool operator ==(other) =>
-      other is TransformerId && other.package == package && other.path == path;
-
-  int get hashCode => package.hashCode ^ path.hashCode;
-
-  /// Returns a serialized form of [this] that can be passed to
-  /// [new TransformerId.parse].
-  String serialize() => path == null ? package : '$package/$path';
-
-  String toString() => serialize();
-
-  /// Returns the asset id for the library identified by this transformer id.
-  ///
-  /// If `path` is null, this will determine which library to load. Unlike
-  /// [getAssetId], this doesn't take generated assets into account; it's used
-  /// to determine transformers' dependencies, which requires looking at files
-  /// on disk.
-  Future<AssetId> getAssetId(Barback barback) {
-    if (path != null) {
-      return new Future.value(new AssetId(package, 'lib/$path.dart'));
-    }
-
-    var transformerAsset = new AssetId(package, 'lib/transformer.dart');
-    return barback.getAssetById(
-        transformerAsset).then(
-            (_) =>
-                transformerAsset).catchError(
-                    (e) => new AssetId(package, 'lib/$package.dart'),
-                    test: (e) => e is AssetNotFoundException);
-  }
-}