message: Profiler: restore correct behavior of StartTracing with empty workers list.
  absl::StrSplit behaves differently from str_util::Split when the passed string is empty. Restore previous behavior by explicitly checking for an empty string.
diff: @@ -201,7 +201,10 @@ Status StartTracing(const tensorflow::string& service_addr,
  constexpr char kProfilePluginDirectory[] = "plugins/profile/";
  tensorflow::string repository_root =
  io::JoinPath(logdir, kProfilePluginDirectory);
  - std::vector<tensorflow::string> hostnames = absl::StrSplit(workers_list, ',');
  + std::vector<tensorflow::string> hostnames;
  + if (!workers_list.empty()) {
  + hostnames = absl::StrSplit(workers_list, ',');
  + }
  TF_RETURN_IF_ERROR(MaybeCreateEmptyEventFile(logdir));
  