Run pub tests against older versions of barback.

third_party/pkg/barback-0.13.0/test/transformer/lazy_rewrite.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.lazy_rewrite;
 
+import 'dart:async';
+
 import 'package:barback/barback.dart';
 
-import 'declaring_rewrite.dart';
+import 'rewrite.dart';
 
 /// Like [RewriteTransformer], but returns a lazy asset that doesn't perform the
 /// rewrite until it's materialized.
-class LazyRewriteTransformer extends DeclaringRewriteTransformer
+class LazyRewriteTransformer extends RewriteTransformer
     implements LazyTransformer {
   LazyRewriteTransformer(String from, String to)
       : super(from, to);
+
+  Future declareOutputs(DeclaringTransform transform) {
+    if (consumePrimary) transform.consumePrimary();
+    for (var extension in to.split(" ")) {
+      var id = transform.primaryId.changeExtension(".$extension");
+      transform.declareOutput(id);
+    }
+  }
 }