message: Fix bug in the default tf.distribute.Strategy where the return value of
  make_input_fn_iterator() did not have an `initialize()` method.
diff: @@ -1685,7 +1685,8 @@ class _DefaultDistributionExtended(DistributionStrategyExtended):
  def _make_input_fn_iterator(self,
  input_fn,
  replication_mode=InputReplicationMode.PER_WORKER):
  - return input_fn(InputContext()).make_initializable_iterator()
  + dataset = input_fn(InputContext())
  + return _DefaultDistributionExtended.DefaultInputIterator(dataset)
  def _experimental_make_numpy_dataset(self, numpy_input, session):
  numpy_flat = nest.flatten(numpy_input)
  