message: Update private API usage of profiler.warmup.
  Copy the content of warmup instead, which is just a start/stop pair.
diff: @@ -2139,7 +2139,9 @@ class TensorBoard(Callback, version_utils.TensorBoardVersionSelector):
  raise ValueError(profile_batch_error_message)
  if self._start_batch > 0:
  - profiler.warmup() # Improve the profiling accuracy.
  + # Warm up and improve the profiling accuracy.
  + profiler.start('')
  + profiler.stop(save=False)
  # True when a trace is running.
  self._is_tracing = False
  