message: Use group_id as step name when no other information is available.
diff: @@ -98,7 +98,7 @@ std::string EventNode::GetGroupName() const {
  if (auto graph_type_stat = GetContextStat(StatType::kGraphType)) {
  name_parts.push_back((*graph_type_stat)->str_value());
  }
  - int64 step_num = 0;
  + int64 step_num = group_id_.value_or(0);
  if (auto step_num_stat = GetContextStat(StatType::kStepNum)) {
  step_num = (*step_num_stat)->int64_value();
  }
  