* `FreeBufferHandle`

* `tf.train.CheckpointOptions` and `tf.saved_model.SaveOptions`
    * These now take in a new argument called `experimental_sharding_callback`.
      This is a callback function wrapper that will be executed to determine how
      tensors will be split into shards when the saver writes the checkpoint
      shards to disk. `tf.train.experimental.ShardByTaskPolicy` is the default