message: Register XlaSharding op to PFor
  It is the same as tf.identity except that there is a sharding attribute to pass
  to XLA.
diff: @@ -2902,6 +2902,13 @@ def _convert_cwise(pfor_input, op_type, op_func):
  return wrap(op_func(*[x.t for x in pfor_input.inputs]), True)
  +@RegisterPFor("XlaSharding")
  +def _convert_xla_sharding(pfor_input):
  + t = pfor_input.stacked_input(0)
  + sharding = pfor_input.get_attr("sharding")
  + return wrap(xla.sharding(t, sharding=sharding), True)
  +
  +
  @RegisterPFor("LeakyRelu")
  def _convert_leaky_relu(pfor_input):
  t = pfor_input.stacked_input(0)
  