*   Add a `tf.distribute.cluster_resolver.TPUClusterResolver.connect` API to
    simplify TPU initialization.
*   Add `tf.distribute.Strategy.gather` and
    `tf.distribute.ReplicaContext.all_gather` methods to gather and concatenate
    `tf.distribute.DistributedValues` across workers and devices.

### `tf.keras`:

*   Introduces experimental preprocessing layers API

# kernel registration - REGISTER_OP, REGISTER_KERNEL_BUILDER, etc.
#
# This setting is currently experimental. The 'v2' implementation does _not_
# correspond to a particular, finalized design; rather, it relates to
# developing one.
#
# The current aim of the 'v2' implementation is to allow 'unused' ops and
# kernels to be discarded by the linker (to the benefit of binary size).
bool_flag(

# the dependencies of that target which include a license notice file are then
# included when generating that license. Necessary because the license targets
# in TensorFlow are manually enumerated rather than generated automatically.
do_external_licenses_check(){
  BUILD_TARGET="$1"
  LICENSES_TARGET="$2"

  # grep patterns for targets which are allowed to be missing from the licenses