Run pub tests against older versions of barback.

third_party/pkg/barback-0.13.0/test/transformer/lazy_rewrite.dart

Index: third_party/pkg/barback-0.13.0/test/transformer/lazy_rewrite.dart
diff --git a/pkg/barback/test/transformer/lazy_rewrite.dart b/third_party/pkg/barback-0.13.0/test/transformer/lazy_rewrite.dart
similarity index 59%
copy from pkg/barback/test/transformer/lazy_rewrite.dart
copy to third_party/pkg/barback-0.13.0/test/transformer/lazy_rewrite.dart
index 63bffb607a1ff6f456fb0ce5149180b049a15fbf..1a3677877684151bb3e210fe6c190b7030981956 100644
--- a/pkg/barback/test/transformer/lazy_rewrite.dart
+++ b/third_party/pkg/barback-0.13.0/test/transformer/lazy_rewrite.dart
@@ -4,14 +4,24 @@
 
 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);
+    }
+  }
 }