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

sdk/lib/_internal/pub_generated/asset/dart/transformer_isolate.dart

Index: sdk/lib/_internal/pub_generated/asset/dart/transformer_isolate.dart
diff --git a/sdk/lib/_internal/pub_generated/asset/dart/transformer_isolate.dart b/sdk/lib/_internal/pub_generated/asset/dart/transformer_isolate.dart
deleted file mode 100644
index 50bb97baac869e1a1ca8666246a6d312158efbed..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/asset/dart/transformer_isolate.dart
+++ /dev/null
@@ -1,112 +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.asset.transformer_isolate;
-
-import 'dart:convert';
-import 'dart:isolate';
-import 'dart:mirrors';
-
-import 'package:barback/barback.dart';
-
-import 'serialize.dart';
-
-/// The mirror system.
-///
-/// Cached to avoid re-instantiating each time a transformer is initialized.
-final _mirrors = currentMirrorSystem();
-
-/// Sets up the initial communication with the host isolate.
-void loadTransformers(SendPort replyTo) {
-  var port = new ReceivePort();
-  replyTo.send(port.sendPort);
-  port.listen((wrappedMessage) {
-    // TODO(nweiz): When issue 19228 is fixed, spin up a separate isolate for
-    // libraries loaded beyond the first so they can run in parallel.
-    respond(wrappedMessage, (message) {
-      var configuration = JSON.decode(message['configuration']);
-      var mode = new BarbackMode(message['mode']);
-      return _initialize(message['library'], configuration, mode).
-          map(serializeTransformerLike).toList();
-    });
-  });
-}
-
-/// Loads all the transformers and groups defined in [uri].
-///
-/// Loads the library, finds any [Transformer] or [TransformerGroup] subclasses
-/// in it, instantiates them with [configuration] and [mode], and returns them.
-List _initialize(String uri, Map configuration, BarbackMode mode) {
-  var transformerClass = reflectClass(Transformer);
-  var aggregateClass = _aggregateTransformerClass;
-  var groupClass = reflectClass(TransformerGroup);
-
-  var seen = new Set();
-  var transformers = [];
-
-  loadFromLibrary(library) {
-    if (seen.contains(library)) return;
-    seen.add(library);
-
-    // Load transformers from libraries exported by [library].
-    for (var dependency in library.libraryDependencies) {
-      if (!dependency.isExport) continue;
-      loadFromLibrary(dependency.targetLibrary);
-    }
-
-    // TODO(nweiz): if no valid transformers are found, throw an error message
-    // describing candidates and why they were rejected.
-    transformers.addAll(library.declarations.values.map((declaration) {
-      if (declaration is! ClassMirror) return null;
-      var classMirror = declaration;
-      if (classMirror.isPrivate) return null;
-      if (classMirror.isAbstract) return null;
-      if (!classMirror.isSubtypeOf(transformerClass) &&
-          !classMirror.isSubtypeOf(groupClass) &&
-          (aggregateClass == null ||
-              !classMirror.isSubtypeOf(aggregateClass))) {
-        return null;
-      }
-
-      var constructor = _getConstructor(classMirror, 'asPlugin');
-      if (constructor == null) return null;
-      if (constructor.parameters.isEmpty) {
-        if (configuration.isNotEmpty) return null;
-        return classMirror.newInstance(const Symbol('asPlugin'), []).reflectee;
-      }
-      if (constructor.parameters.length != 1) return null;
-
-      return classMirror.newInstance(const Symbol('asPlugin'),
-          [new BarbackSettings(configuration, mode)]).reflectee;
-    }).where((classMirror) => classMirror != null));
-  }
-
-  var library = _mirrors.libraries[Uri.parse(uri)];
-
-  // This should only happen if something's wrong with the logic in pub itself.
-  // If it were user error, the entire isolate would fail to load.
-  if (library == null) throw "Couldn't find library at $uri.";
-
-  loadFromLibrary(library);
-  return transformers;
-}
-
-// TODO(nweiz): clean this up when issue 13248 is fixed.
-MethodMirror _getConstructor(ClassMirror classMirror, String constructor) {
-  var name = new Symbol("${MirrorSystem.getName(classMirror.simpleName)}"
-      ".$constructor");
-  var candidate = classMirror.declarations[name];
-  if (candidate is MethodMirror && candidate.isConstructor) return candidate;
-  return null;
-}
-
-// Older barbacks don't support [AggregateTransformer], and calling
-// [reflectClass] on an undefined class will throw an error, so we just define a
-// null getter for them.
-//# if barback >=0.14.1
-ClassMirror get _aggregateTransformerClass =>
-    reflectClass(AggregateTransformer);
-//# else
-//>   ClassMirror get _aggregateTransformerClass => null;
-//# end