message: [TFXLA] Add grad_state for TPUReplicateContext
diff: @@ -146,6 +146,14 @@ class TPUReplicateContext(control_flow_ops.ControlFlowContext):
  if self._outer_context:
  self._outer_context.AddInnerOp(op)
  + @property
  + def grad_state(self):
  + # Define the gradient loop state associated with the TPUReplicateContext to
  + # be None as the TPUReplicateContext does not get nested nor does the
  + # grad_state outside the TPUReplicateContext affect the graph inside so the
  + # grad_state should be as if this is the top-level gradient state.
  + return None
  +
  def replicate(computation,
  inputs=None,
  