message: Temporarily allow multiple revived_type registrations.
diff: @@ -132,7 +132,9 @@ def register_revived_type(identifier, predicate, versions):
  "Got multiple registrations with version {} for type {}".format(
  registration.version, identifier))
  version_numbers.add(registration.version)
  - if identifier in _REVIVED_TYPE_REGISTRY:
  + # TODO(kathywu): Remove the "optimizer" special case here after the Keras
  + # repo optimizer registration has been submitted.
  + if identifier in _REVIVED_TYPE_REGISTRY and identifier != "optimizer":
  raise AssertionError(
  "Duplicate registrations for type {}".format(identifier))
  