layers without the original class definition, but if this isn't required the
    tracing can be disabled with the added option.
*   The `tf.keras.mixed_precision` API is now non-experimental. The
    non-experimental API differs from the experimental API in several ways.
    *   `tf.keras.mixed_precision.Policy` no longer takes in a
        `tf.mixed_precision. experimental.LossScale` in the constructor, and no