Make pub strong-mode clean.

lib/src/barback/foreign_transformer.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.
 
 import 'dart:async';
 import 'dart:isolate';
 
 import 'package:barback/barback.dart';
 
 import '../asset/dart/serialize.dart';
@@ skipping 105 matching lines @@
 }
 
 /// A wrapper for a transformer group that's in a different isolate.
 class _ForeignGroup implements TransformerGroup {
   final Iterable<Iterable> phases;
 
   /// The result of calling [toString] on the transformer group in the isolate.
   final String _toString;
 
   _ForeignGroup(TransformerConfig config, Map map)
-      : phases = map['phases'].map((phase) {
-          return phase.map((transformer) => deserializeTransformerLike(
-              transformer, config)).toList();
+      : phases = (map['phases'] as List).map((phase) {
+          return (phase as List)
+              .map((transformer) =>
+                  deserializeTransformerLike(transformer, config))
+              .toList();
         }).toList(),
         _toString = map['toString'];
 
   String toString() => _toString;
 }
 
 /// Converts a serializable map into a [Transformer], an [AggregateTransformer],
 /// or a [TransformerGroup].
 deserializeTransformerLike(Map map, TransformerConfig config) {
   var transformer;
@@ skipping 20 matching lines @@
     default: assert(false);
   }
 
   if (transformer is Transformer) {
     return ExcludingTransformer.wrap(transformer, config);
   } else {
     assert(transformer is AggregateTransformer);
     return ExcludingAggregateTransformer.wrap(transformer, config);
   }
 }