Add support for transformer clusters to barback.

pkg/barback/test/utils.dart

Index: pkg/barback/test/utils.dart
diff --git a/pkg/barback/test/utils.dart b/pkg/barback/test/utils.dart
index 7fb1a23b0ee4da94378de14c4d6ff163bf4135f7..85a9c6179942238b1288ed9aee4c407bec67d49e 100644
--- a/pkg/barback/test/utils.dart
+++ b/pkg/barback/test/utils.dart
@@ -88,7 +88,7 @@ void initGraph([assets,
   _barback = new Barback(_provider);
   _nextBuildResult = 0;
 
-  transformers.forEach(_barback.updateTransformers);
+  transformers.forEach(_barback.updateOperators);
 
   // There should be one successful build after adding all the transformers but
   // before adding any sources.
@@ -131,11 +131,11 @@ void removeSources(Iterable assets) {
 void removeSourcesSync(Iterable assets) =>
     _barback.removeSources(_parseAssets(assets));
 
-/// Sets the transformers for [package] to [transformers].
-void updateTransformers(String package,
-    Iterable<Iterable<Transformer>> transformers) {
-  schedule(() => _barback.updateTransformers(package, transformers),
-      "updating transformers for $package");
+/// Sets the operators for [package] to [operators].
+void updateOperators(String package,
+    Iterable<Iterable<Operator>> operators) {
+  schedule(() => _barback.updateOperators(package, operators),
+      "updating operators for $package");
 }
 
 /// Parse a list of strings or [AssetId]s into a list of [AssetId]s.