*   <THIS SECTION SHOULD CONTAIN API, ABI AND BEHAVIORAL BREAKING CHANGES>

*   `tf.summary.trace_on` now takes a `profiler_outdir` argument. This must be
    set if `profiler` arg is set to `True`.

    *   `tf.summary.trace_export`'s `profiler_outdir` arg is now a no-op.
        Enabling the profiler now requires setting `profiler_outdir` in
        `trace_on`.

*   `tf.estimator`

    *   The tf.estimator API is removed.