message: Fix build broken by signed/unsigned comparisons.
diff: @@ -110,7 +110,7 @@ Status HostTracer::CollectData(RunMetadata* run_metadata) {
  constexpr char kUserMetadataMarker = '#';
  for (TraceMeRecorder::ThreadEvents& thread : events_) {
  - int32 thread_id = thread.thread.tid;
  + uint32_t thread_id = thread.thread.tid;
  thread_names->insert({thread_id, thread.thread.name});
  for (TraceMeRecorder::Event& event : thread.events) {
  if (event.start_time && event.end_time) {
  