Only pass an AssetId to isPrimary and declareOutputs.

pkg/barback/test/transformer/lazy_many_to_one.dart

Index: pkg/barback/test/transformer/lazy_many_to_one.dart
diff --git a/pkg/barback/test/transformer/lazy_many_to_one.dart b/pkg/barback/test/transformer/lazy_many_to_one.dart
index 7e1b1141d2e9567079c62d35c4ee1a8f0da53ccd..dcdc0b16b31c0743931b238d3dab161eab266ed5 100644
--- a/pkg/barback/test/transformer/lazy_many_to_one.dart
+++ b/pkg/barback/test/transformer/lazy_many_to_one.dart
@@ -18,6 +18,6 @@ class LazyManyToOneTransformer extends ManyToOneTransformer
       : super(extension);
 
   Future declareOutputs(DeclaringTransform transform) {
-    transform.declareOutput(transform.primaryInput.id.changeExtension(".out"));
+    transform.declareOutput(transform.primaryId.changeExtension(".out"));
   }
 }