message: Update the step marker format.
diff: @@ -1090,11 +1090,11 @@ class Model(base_layer.Layer, version_utils.ModelVersionSelector):
  with data_handler.catch_stop_iteration():
  for step in data_handler.steps():
  with trace.Trace(
  - 'TraceContext',
  - graph_type='train',
  + 'train',
  epoch_num=epoch,
  step_num=step,
  - batch_size=batch_size):
  + batch_size=batch_size,
  + _r=1):
  callbacks.on_train_batch_begin(step)
  tmp_logs = train_function(iterator)
  if data_handler.should_sync:
  @@ -1378,7 +1378,7 @@ class Model(base_layer.Layer, version_utils.ModelVersionSelector):
  self.reset_metrics()
  with data_handler.catch_stop_iteration():
  for step in data_handler.steps():
  - with trace.Trace('TraceContext', graph_type='test', step_num=step):
  + with trace.Trace('test', step_num=step, _r=1):
  callbacks.on_test_batch_begin(step)
  tmp_logs = test_function(iterator)
  if data_handler.should_sync:
  