message: [tf.data service] Add a comment to clarify how workers manage tasks.
diff: @@ -101,7 +101,8 @@ class DataServiceWorkerImpl {
  mutex mu_;
  condition_variable cv_;
  - // Information about tasks, keyed by task ids.
  + // Information about tasks, keyed by task ids. The tasks are updated based on
  + // the heartbeat responses from the dispatcher.
  absl::flat_hash_map<int64, std::shared_ptr<Task>> tasks_ TF_GUARDED_BY(mu_);
  // Ids of tasks that have finished.
  absl::flat_hash_set<int64> finished_tasks_ TF_GUARDED_BY(mu_);
  