message: [Profiler] Fix macos build.
diff: @@ -47,7 +47,8 @@ void CombinePerCoreStepInfo(
  // Since we have assigned a new step number to the combined result, update
  // the step number on each core to this new step number.
  uint32 new_step_num = dst->step_num();
  - for (auto& [_, stepinfo] : *dst->mutable_step_info_per_core()) {
  + for (auto& percore_stepinfo : *dst->mutable_step_info_per_core()) {
  + auto& stepinfo = percore_stepinfo.second;
  stepinfo.set_step_num(new_step_num);
  }
  