Make Transform a little more pleasant to use:

pkg/barback/test/transformer/many_to_one.dart

Index: pkg/barback/test/transformer/many_to_one.dart
diff --git a/pkg/barback/test/transformer/many_to_one.dart b/pkg/barback/test/transformer/many_to_one.dart
index 59a190cf9400072ad88d68fd0265984d756f6762..56f64640147db0f0171f6f77077a5df28bae01f0 100644
--- a/pkg/barback/test/transformer/many_to_one.dart
+++ b/pkg/barback/test/transformer/many_to_one.dart
@@ -27,21 +27,19 @@ class ManyToOneTransformer extends MockTransformer {
     new Future.value(asset.id.extension == ".$extension");
 
   Future doApply(Transform transform) {
-    return getPrimary(transform)
-        .then((primary) => primary.readAsString())
-        .then((contents) {
+    return transform.primaryInput.readAsString().then((contents) {
       // Get all of the included inputs.
       return Future.wait(contents.split(",").map((path) {
         var id;
         if (path.contains("|")) {
           id = new AssetId.parse(path);
         } else {
-          id = new AssetId(transform.primaryId.package, path);
+          id = new AssetId(transform.primaryInput.id.package, path);
         }
         return getInput(transform, id).then((input) => input.readAsString());
       }));
     }).then((outputs) {
-      var id = transform.primaryId.changeExtension(".out");
+      var id = transform.primaryInput.id.changeExtension(".out");
       transform.addOutput(new Asset.fromString(id, outputs.join()));
     });
   }