Method ProjectKeys

common/legacy_value.cc:236–241

 private:
  absl::Status ProjectKeys(google::protobuf::Arena* arena) {
    if (cel_list_.ok() && *cel_list_ == nullptr) {
      cel_list_ = cel_map_->ListKeys(arena);
    }
    return cel_list_.status();
  }

  const CelMap* const cel_map_;
  const int size_ = 0;