Expose aggregate transformers in barback.

pkg/barback/test/transformer/mock.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.test.transformer.mock;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'package:barback/src/utils.dart';
@@ skipping 12 matching lines @@
   /// The number of times the transformer has been applied.
   ///
   /// This is scheduled. The Future will complete at the point in the schedule
   /// that this is called.
   Future<int> get numRuns => schedule(() => _numRuns);
   var _numRuns = 0;
 
   /// The number of currently running transforms.
   int _runningTransforms = 0;
 
-  /// A completer for pausing the transformer before it finishes running [apply].
+  /// A completer for pausing the transformer before it finishes running
+  /// [apply].
   Completer _apply;
 
   /// Completers for pausing the transformer before it finishes running
   /// [isPrimary].
   final _isPrimary = new Map<AssetId, Completer>();
 
   /// Completers for pausing the transformer before it finishes getting inputs
   /// the [Transform].
   final _getInput = new Map<AssetId, Completer>();
 
@@ skipping 150 matching lines @@
   /// This may return a `Future<bool>` or, if it's entirely synchronous, a
   /// `bool`.
   doIsPrimary(AssetId id);
 
   /// The wrapped version of [doApply] for subclasses to override.
   ///
   /// If this does asynchronous work, it should return a [Future] that completes
   /// once it's finished.
   doApply(Transform transform);
 }