See the HTTPBackendRef definition for the rules about what makes a single
                        HTTPBackendRef invalid.


                        When a HTTPBackendRef is invalid, 500 status codes MUST be returned for
                        requests that would have otherwise been routed to an invalid backend. If
                        multiple backends are specified, and some are invalid, the proportion of

*   `tf.random`:
    * Added `tf.random.experimental.index_shuffle`, for shuffling a sequence without materializing the sequence in memory.

*   `tf.RaggedTensor`:
    *   Introduced `tf.experimental.RowPartition`, which encodes how one dimension in a RaggedTensor relates to another, into the public API.
    *   Introduced `tf.experimental.DynamicRaggedShape`, which represents the shape of a RaggedTensor.

## Security