Enable re-export in docgen. Work in progress. More to come.

pkg/barback/lib/barback.dart

 // 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 barback;
 
+import 'src/transform.dart';
+import 'src/transformer.dart';
+
 export 'src/asset.dart';
 export 'src/asset_id.dart';
 export 'src/asset_set.dart';
 export 'src/barback.dart';
 export 'src/barback_settings.dart';
 export 'src/build_result.dart';
 export 'src/errors.dart' hide flattenAggregateExceptions;
 export 'src/log.dart';
 export 'src/package_provider.dart';
 export 'src/transform.dart' show Transform;
 export 'src/transform_logger.dart';
 export 'src/transformer.dart';
 export 'src/transformer_group.dart';