message: Fix OSS TPUClusterResolver `get_tpu_system_metadata` method.
diff: @@ -221,7 +221,20 @@ class TPUClusterResolver(cluster_resolver.ClusterResolver):
  return self.task_type
  def get_tpu_system_metadata(self):
  - """Retrieves TPU system metadata given a TPUClusterResolver."""
  + """Returns the metadata of the TPU system.
  +
  + Users can call this method to get some facts of the TPU system, like
  + total number of cores, number of TPU workers and the devices. E.g.
  + ```python
  +
  + resolver = tf.distribute.cluster_resolver.TPUClusterResolver(tpu='')
  + tpu_system_medata = resolver.get_tpu_system_metadata()
  + num_hosts = tpu_system_medata.num_hosts
  + ```
  +
  + Returns:
  + A `tf.tpu.experimental.TPUSystemMetadata` object.
  + """
  cluster_spec = self.cluster_spec()
  cluster_def = cluster_spec.as_cluster_def() if cluster_spec else None
  tpu_system_metadata = (
  @@ -230,6 +243,8 @@ class TPUClusterResolver(cluster_resolver.ClusterResolver):
  cluster_def=cluster_def,
  query_topology=False))
  + return tpu_system_metadata
  +
  def cluster_spec(self):
  """Returns a ClusterSpec object based on the latest TPU information.
  