Roll to pickup pool changes

packages/barback/lib/src/transformer/wrapping_aggregate_transformer.dart

Index: packages/barback/lib/src/transformer/wrapping_aggregate_transformer.dart
diff --git a/packages/barback/lib/src/transformer/wrapping_aggregate_transformer.dart b/packages/barback/lib/src/transformer/wrapping_aggregate_transformer.dart
index a24260da3f4acb79e0d2ca6b704c596f4ce528a1..8d65ae07bb584bcffcd82425dc58e92aa2d0e536 100644
--- a/packages/barback/lib/src/transformer/wrapping_aggregate_transformer.dart
+++ b/packages/barback/lib/src/transformer/wrapping_aggregate_transformer.dart
@@ -60,11 +60,8 @@ class WrappingAggregateTransformer implements AggregateTransformer {
 class _DeclaringWrappingAggregateTransformer
     extends WrappingAggregateTransformer
     implements DeclaringAggregateTransformer {
-  final DeclaringTransformer _declaring;
-
   _DeclaringWrappingAggregateTransformer(DeclaringTransformer transformer)
-      : _declaring = transformer,
-        super._(transformer as Transformer);
+      : super._(transformer as Transformer);
 
   Future declareOutputs(DeclaringAggregateTransform aggregateTransform) {
     return newDeclaringTransform(aggregateTransform).then((transform) {