message: TF API Fixit: Remove private usage of AggregatingVariable.
  This avoids the special logic in autocast_variable for AggregatingVariable as AggregatingVariable is a private concept in tf.distribute that Keras should not need to be aware of.
diff: """Contains AutoCastVariable, a variable which automatically casts itself."""
  import threading
  -from tensorflow.python.distribute import ps_values as ps_distribute_values
  from tensorflow.python.eager import context
  from tensorflow.python.framework import ops
  from tensorflow.python.keras.distribute import distributed_training_utils
  @@ -509,8 +508,7 @@ def create_autocast_variable(variable):
  Returns:
  An AutoCastVariable that wraps the variable.
  """
  - if ((not distributed_training_utils.is_distributed_variable(variable)) and
  - not isinstance(variable, ps_distribute_values.AggregatingVariable)):
  + if not distributed_training_utils.is_distributed_variable(variable):
  return AutoCastVariable(variable)
  class AutoCastDistributedVariable(AutoCastVariable, variable.__class__):
  @@ -521,11 +519,6 @@ def create_autocast_variable(variable):
  """
  def __repr__(self):
  - if issubclass(ps_distribute_values.AggregatingVariable,
  - variable.__class__):
  - # AggregatingVariable's __repr__ simply calls super.__repr__. So we do
  - # the same here for consistency, which calls AutoCastVariable.__repr__.
  - return super(AutoCastDistributedVariable, self).__repr__()
  # pylint: disable=missing-format-attribute
  return ('<AutoCastDistributedVariable dtype={v.dtype.name} '
  