message: [tf.data] Fix memory leak in to_tf_record_op.
diff: @@ -87,6 +87,7 @@ class ToTFRecordOp : public AsyncOpKernel {
  IteratorContext iter_ctx(std::move(params));
  DatasetBase* finalized_dataset;
  TF_RETURN_IF_ERROR(FinalizeDataset(ctx, dataset, &finalized_dataset));
  + core::ScopedUnref unref(finalized_dataset);
  std::unique_ptr<IteratorBase> iterator;
  TF_RETURN_IF_ERROR(finalized_dataset->MakeIterator(
  