message: [tf.data service] Update standalone iterator name from "iterator" to "Iterator".
  This makes it consistent with regular tf.data iterators, so xprof tooling can treat them the same.
diff: @@ -124,7 +124,7 @@ Status Dataset::MakeIterator(std::unique_ptr<SplitProvider> split_provider,
  // Create the iterator from the dataset.
  std::unique_ptr<IteratorBase> iterator;
  TF_RETURN_IF_ERROR(dataset_->MakeIterator(ctx.get(), /*parent=*/nullptr,
  - "iterator", &iterator));
  + "Iterator", &iterator));
  *result = WrapUnique(new Iterator(iterator.release(), ctx.release()));
  