message: Replace private method call _ref() with read_value()
diff: @@ -109,7 +109,7 @@ class VariableClippingOptimizer(optimizer.Optimizer):
  def _clip_dense(self, var):
  with self._maybe_colocate_with(var):
  - updated_var_value = var._ref() # pylint: disable=protected-access
  + updated_var_value = var.read_value()
  normalized_var = clip_ops.clip_by_norm(
  updated_var_value, self._max_norm, self._vars_to_clip_dims[var])
  delta = updated_var_value - normalized_var
  