Roll to pickup pool changes

packages/barback/test/transformer/mock_aggregate.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.test.transformer.mock_aggregate;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'package:barback/src/utils.dart';
@@ skipping 33 matching lines @@
   final _getInput = new Map<AssetId, Completer>();
 
   /// Completer for pausing the transformer before it accesses
   /// [getPrimaryInputs].
   Completer _primaryInputs;
 
   /// A completer that completes once this transformer begins running.
   ///
   /// Once this transformer finishes running, this is reset to a new completer,
   /// so it can be used multiple times.
-  var _started = new Completer();
+  var _started = new Completer<Null>();
 
   /// `true` if any transforms are currently running.
   ///
   /// This is scheduled. The Future will complete at the point in the schedule
   /// that this is called.
   Future<bool> get isRunning => schedule(() => _runningTransforms > 0);
 
   /// All elements of this set will be automatically consumed during [apply].
   final consumePrimaries = new Set<String>();
 
@@ skipping 129 matching lines @@
   /// This may return a `Future<String>` or, if it's entirely synchronous, a
   /// `String`.
   doClassifyPrimary(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(AggregateTransform transform);
 }