Remove barback from the repo.

pkg/barback/lib/src/transformer/declaring_transform.dart

-// 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 barback.transformer.declaring_transform;
-
-import 'dart:async';
-
-import '../asset/asset_id.dart';
-import 'declaring_aggregate_transform.dart';
-import 'transform_logger.dart';
-
-/// Creates a new [DeclaringTransform] wrapping an
-/// [AggregateDeclaringTransform].
-///
-/// Although barback internally works in terms of
-/// [DeclaringAggregateTransformer]s, most transformers only work on individual
-/// primary inputs in isolation. We want to allow those transformers to
-/// implement the more user-friendly [DeclaringTransformer] interface which
-/// takes the more user-friendly [DeclaringTransform] object. This method wraps
-/// the more general [DeclaringAggregateTransform] to return a
-/// [DeclaringTransform] instead.
-Future<DeclaringTransform> newDeclaringTransform(
-    DeclaringAggregateTransform aggregate) {
-  // A wrapped [Transformer] will assign each primary input a unique transform
-  // key, so we can safely get the first asset emitted. We don't want to wait
-  // for the stream to close, since that requires barback to prove that no more
-  // new assets will be generated.
-  return aggregate.primaryIds.first.then((primaryId) => 
-      new DeclaringTransform._(aggregate, primaryId));
-}
-
-/// A transform for [DeclaringTransformer]s that allows them to declare the ids
-/// of the outputs they'll generate without generating the concrete bodies of
-/// those outputs.
-class DeclaringTransform {
-  /// The underlying aggregate transform.
-  final DeclaringAggregateTransform _aggregate;
-
-  final AssetId primaryId;
-
-  /// A logger so that the [Transformer] can report build details.
-  TransformLogger get logger => _aggregate.logger;
-
-  DeclaringTransform._(this._aggregate, this.primaryId);
-
-  /// Stores [id] as the id of an output that will be created by this
-  /// transformation when it's run.
-  ///
-  /// A transformation can declare as many assets as it wants. If
-  /// [DeclaringTransformer.declareOutputs] declareds a given asset id for a
-  /// given input, [Transformer.apply] should emit the corresponding asset as
-  /// well.
-  void declareOutput(AssetId id) => _aggregate.declareOutput(id);
-
-  /// Consume the primary input so that it doesn't get processed by future
-  /// phases or emitted once processing has finished.
-  ///
-  /// Normally the primary input will automatically be forwarded unless the
-  /// transformer overwrites it by emitting an input with the same id. This
-  /// allows the transformer to tell barback not to forward the primary input
-  /// even if it's not overwritten.
-  void consumePrimary() => _aggregate.consumePrimary(primaryId);
-}