message: Add loop b_sync control trigger nodes to the outer context via AddInnerOp.
diff: @@ -791,6 +791,8 @@ class GradLoopState(object):
  self._grad_sync = control_trigger(name="b_sync")
  self._grad_sync._set_control_flow_context(self._grad_context)
  self._grad_index.op._add_control_input(self._grad_sync)
  + if self._grad_context.outer_context:
  + self._grad_context.outer_context.AddInnerOp(self._grad_sync)
  return self._grad_sync
  @property
  