Code transformers fixes for latest analyzer update

pkg/code_transformers/lib/src/resolvers.dart

Index: pkg/code_transformers/lib/src/resolvers.dart
diff --git a/pkg/code_transformers/lib/src/resolvers.dart b/pkg/code_transformers/lib/src/resolvers.dart
index f7e39b3de595cca935fbb830ad076013070c51bf..077ea5b25ba3dbeda554332b37672773c1c8f3d5 100644
--- a/pkg/code_transformers/lib/src/resolvers.dart
+++ b/pkg/code_transformers/lib/src/resolvers.dart
@@ -68,9 +68,10 @@ abstract class ResolverTransformer implements Transformer {
   ///    }
   Future applyToEntryPoints(Transform transform, [List<AssetId> entryPoints]) {
     return resolvers.get(transform, entryPoints).then((resolver) {
-      return new Future.value(applyResolver(transform, resolver)).then((_) {
-        resolver.release();
-      });
+      return new Future(() => applyResolver(transform, resolver))
+        .whenComplete(() {
+          resolver.release();
+        });
     });
   }