eager-friendly training step inside of a `tf.function`. With this
    *   All input types are converted to `Dataset`.
    *   The path assumes there is always a distribution strategy. when
        distribution strategy is not specified the path uses a no-op
        distribution strategy.
    *   The training step is wrapped in `tf.function` unless `run_eagerly=True`
        is set in compile. The single path execution code does not yet support

                                          type: integer
                                        description: Map of upstream localities to
                                          traffic distribution weights.
                                        type: object
                                    type: object
                                  type: array
                                enabled: