message: TF train: allow passing in run_metadata to unblock tf profiler.
diff: @@ -484,7 +484,8 @@ def train(train_op,
  save_checkpoint_secs=600,
  save_summaries_steps=100,
  config=None,
  - max_wait_secs=7200):
  + max_wait_secs=7200,
  + run_metadata=None):
  """Runs the training loop.
  Args:
  @@ -511,6 +512,7 @@ def train(train_op,
  become available. This should be kept relatively short to help detect
  incorrect code, but sometimes may need to be increased if the chief takes
  a while to start up.
  + run_metadata: A [`RunMetadata`] protocol buffer.
  Returns:
  the value of the loss function after training.
  @@ -541,5 +543,5 @@ def train(train_op,
  max_wait_secs=max_wait_secs) as session:
  loss = None
  while not session.should_stop():
  - loss = session.run(train_op)
  + loss = session.run(train_op, run_metadata=run_metadata)
  return loss
  