message: Fix tpu_strategy.py's corner bug which may add list with tuple b/c `DistributedValues.values` actually returns tuple.
diff: @@ -1172,7 +1172,7 @@ class TPUExtended(distribute_lib.StrategyExtendedV1):
  if not isinstance(value, values.DistributedValues):
  return value
  - value_list = value.values
  + value_list = list(value.values)
  # pylint: disable=protected-access
  if isinstance(
  value,
  