*   Expose `tf.distribute.Strategy as the new name for
        tf.contrib.distribute.DistributionStrategy.
    *   Migrate linear optimizer from contrib to core.
    *   Move `tf.contrib.signal` to `tf.signal` (preserving aliases in
        tf.contrib.signal).
    *   Users of `tf.contrib.estimator.export_all_saved_models` and related
        should switch to
        `tf.estimator.Estimator.experimental_export_all_saved_models`.
*   tf.data: