Step 1 of rename cross_tower_ops -> cross_device_ops in

`MirroredStrategy.__init__()`.

PiperOrigin-RevId: 218755068

tensorflow/contrib/distribute/python/mirrored_strategy.py

@@ -346,24 +346,27 @@ class MirroredStrategy(distribute_lib.DistributionStrategy):
     num_gpus_per_worker: number of GPUs per worker. This is the same as
       `num_gpus` and only one of `num_gpus` and `num_gpus_per_worker` can be
       specified.
-    cross_tower_ops: optional, a descedant of `CrossDeviceOps`. If this is not
+    cross_device_ops: optional, a descedant of `CrossDeviceOps`. If this is not
       set, the `configure` method will try to find the best one.
     prefetch_on_device: optional boolean to specify whether to prefetch input
       data to devices.
     auto_shard_dataset: whether to auto-shard the dataset when there are
       multiple workers.
+    cross_tower_ops: Deprecated alias for `cross_device_ops`.
   """
 
   def __init__(self,
                devices=None,
                num_gpus=None,
                num_gpus_per_worker=None,
-               cross_tower_ops=None,
+               cross_device_ops=None,
                prefetch_on_device=None,
-               auto_shard_dataset=False):
+               auto_shard_dataset=False,
+               cross_tower_ops=None):
     super(MirroredStrategy, self).__init__()
 
-    self._cross_tower_ops = cross_tower_ops
+    assert not (cross_device_ops and cross_tower_ops)
+    self._cross_tower_ops = cross_device_ops or cross_tower_ops
     self._prefetch_on_device = prefetch_on_device
     self._auto_shard_dataset = auto_shard_dataset
     # Remember num GPUs which might be needed by `configure` method.