message: Fix symbol name in `Layer.add_metric`.
diff: @@ -1660,8 +1660,8 @@ class Layer(module.Module, version_utils.LayerVersionSelector):
  self.mean = tf.keras.metrics.Mean(name='metric_1')
  def call(self, inputs):
  - self.add_metric(self.mean(x))
  - self.add_metric(tf.reduce_sum(x), name='metric_2')
  + self.add_metric(self.mean(inputs))
  + self.add_metric(tf.reduce_sum(inputs), name='metric_2')
  return inputs
  ```
  