Transition barback's infrastructure to an aggregate-based model.

pkg/barback/lib/src/transformer/aggregate_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.aggregate_transform;
 
 import 'dart:async';
 import 'dart:convert';
 
 import '../asset/asset.dart';
@@ skipping 114 matching lines @@
   }
 }
 
 /// The controller for [AggregateTransform].
 class AggregateTransformController extends BaseTransformController {
   AggregateTransform get transform => super.transform;
 
   /// The set of assets that the transformer has emitted.
   AssetSet get outputs => transform._outputs;
 
-  /// The controller for the [AggregateTransform.primaryInputs] stream.
-  StreamController<Asset> get inputController => transform._inputController;
+  bool get isDone => transform._inputController.isClosed;
 
   AggregateTransformController(TransformNode node)
       : super(new AggregateTransform._(node));
 
-  void close() {
-    super.close();
+  /// Adds a primary input asset to the [AggregateTransform.primaryInputs]
+  /// stream.
+  void addInput(Asset input) => transform._inputController.add(input);
+
+  /// Returns whether an input with the given [id] was added via [addInput].
+  bool addedId(AssetId id) {
+    return transform._emittedPrimaryInputs.ids.contains(id);
+  }
+
+  void done() {
     transform._inputController.close();
   }
 }