Stop working around issue 14971 in barback.

pkg/barback/lib/src/serialize.dart

Index: pkg/barback/lib/src/serialize.dart
diff --git a/pkg/barback/lib/src/serialize.dart b/pkg/barback/lib/src/serialize.dart
index 7114039e44d5cc417baf8dfc62a97400619447c3..adc365d6b74f0fcd514e99628afd0390f259fd91 100644
--- a/pkg/barback/lib/src/serialize.dart
+++ b/pkg/barback/lib/src/serialize.dart
@@ -45,10 +45,8 @@ Stream deserializeStream(SendPort sendPort) {
   return callbackStream(() {
     var receivePort = new ReceivePort();
     sendPort.send(receivePort.sendPort);
-    // TODO(nweiz): use a const constructor for StreamTransformer when issue
-    // 14971 is fixed.
     return receivePort.transform(
-        new StreamTransformer(_deserializeTransformer));
+        const StreamTransformer(_deserializeTransformer));
   });
 }