Returns a batched event iterator over the run directory event files.

def load_batches(self):
    """Returns a batched event iterator over the run directory event files."""
    event_iterator = self._directory_watcher.Load()
    while True:
      events = []
      event_bytes = 0
      start = time.time()
      for event_proto in event_iterator:
        events.append(event_proto)
        event_bytes += len(event_proto)
        if len(events) >= self._BATCH_COUNT or event_bytes >= self._BATCH_BYTES:
          break
      elapsed = time.time() - start
      logger.debug('RunLoader.load_batch() yielded in %0.3f sec for %s',
                       elapsed, self._subdir)
      if not events:
        return
      yield _EventBatch(
          events=events,
          experiment_name=self._experiment_name,
          run_name=self._run_name)