message: Fixes a backwards compatibility breakage introduced with multi-label AUC wherein some non-keras estimators could no longer use multi-label AUC.
diff: @@ -1824,6 +1824,8 @@ class AUC(Metric):
  self.label_weights = None
  self._built = False
  + if not self.multi_label:
  + self._build(None)
  def _build(self, shape):
  """Initialize TP, FP, TN, and FN tensors, given the shape of the data."""
  @@ -1854,9 +1856,15 @@ class AUC(Metric):
  'false_negatives',
  shape=variable_shape,
  initializer=init_ops.zeros_initializer)
  +
  + if self.multi_label:
  with ops.init_scope():
  + # This should only be necessary for handling v1 behavior. In v2, AUC
  + # should be initialized outside of any tf.functions, and therefore in
  + # eager mode.
  if not context.executing_eagerly():
  K._initialize_variables(K._get_session()) # pylint: disable=protected-access
  +
  self._built = True
  def update_state(self, y_true, y_pred, sample_weight=None):
  