message: Autotune Dataset.map when transforming builtin map with autograph
diff: @@ -191,8 +191,9 @@ def _tf_abs(x):
  def _tf_dataset_abs(x):
  specs = nest.flatten(x.element_spec)
  if len(specs) == 1:
  - return x.map(math_ops.abs)
  - return x.map(lambda *e: nest.map_structure(math_ops.abs, e))
  + return x.map(math_ops.abs, num_parallel_calls=dataset_ops.AUTOTUNE)
  + return x.map(lambda *e: nest.map_structure(math_ops.abs, e),
  + num_parallel_calls=dataset_ops.AUTOTUNE)
  def _py_abs(x):
  @@ -427,7 +428,8 @@ def map_(fn, *iterables):
  def _tf_dataset_map(fn, *iterables):
  - return dataset_ops.DatasetV2.zip(iterables).map(fn)
  + zipped_dataset = dataset_ops.DatasetV2.zip(iterables)
  + return zipped_dataset.map(fn, num_parallel_calls=dataset_ops.AUTOTUNE)
  def _py_map(fn, *iterables):
  