message: Avoid reordering in ports in SwitchGrad for CondContext.
diff: @@ -69,13 +69,12 @@ def _SwitchGrad(op, *grad):
  # meaning the output is not differentiable.
  return None, None
  elif isinstance(op_ctxt, CondContext):
  - good_grad = grad[op_ctxt.branch]
  zero_grad = grad[1 - op_ctxt.branch]
  # At this point, we have created zero_grad guarded by the right switch.
  # Unfortunately, we may still get None here for not trainable data types.
  if zero_grad is None:
  return None, None
  - return merge([good_grad, zero_grad], name="cond_grad")[0], None
  + return merge(grad, name="cond_grad")[0], None
  else:
  false_grad = switch(grad[0], op.inputs[1])[0]
  true_grad = switch(grad[1], op.inputs[1])[1]
  