message: Fix the type to avoid comparison of integers of different signs.
diff: @@ -60,7 +60,7 @@ struct Context final {
  }
  void EnsureNPerThreadStates(int thread_count) {
  - while (per_thread_states.size() < thread_count) {
  + while (per_thread_states.size() < static_cast<std::size_t>(thread_count)) {
  per_thread_states.emplace_back(new PerThreadState);
  }
  }
  