message: Use the same strategy in testEagerDistributionStrategy
  It's not supported to use variables created under one strategy in another
  strategy. This works now but will break after a refactoring.
  get_or_create_global_step() will only create the variable the first time.
diff: @@ -289,16 +289,17 @@ class CheckpointingTests(test.TestCase):
  functools.partial(model, input_value),
  global_step=root.optimizer_step)
  - for training_continuation in range(3):
  strategy = mirrored_strategy.MirroredStrategy()
  with strategy.scope():
  + for training_continuation in range(3):
  model = MyModel()
  optimizer = adam.AdamOptimizer(0.001)
  root = trackable_utils.Checkpoint(
  - optimizer=optimizer, model=model,
  + optimizer=optimizer,
  + model=model,
  optimizer_step=training_util.get_or_create_global_step())
  - root.restore(checkpoint_management.latest_checkpoint(
  - checkpoint_directory))
  + root.restore(
  + checkpoint_management.latest_checkpoint(checkpoint_directory))
  for _ in range(num_training_steps):
  strategy.extended.call_for_each_replica(
  