message: Update derived_timeline.cc
diff: @@ -130,7 +130,7 @@ void DerivedXLineBuilder::ExpandOrAddLevelEvent(const XEvent& event,
  }
  void DerivedXLineBuilder::ResetLastEvents(int level) {
  - for (int i = level; i < static_cast<int>(last_event_by_level_.size()); ++i) {
  + for (int i = level, iter_limit = last_event_by_level_.size(); i < iter_limit; ++i) {
  last_event_by_level_[i] = absl::nullopt;
  }
  if (level == 0) ResetDependentLines();
  