Creates a JSON-able representation of this object.

    Returns:
      A dictionary mapping (device, tensor name) to JSON-able object
      representations of NumericsAlertHistory.

def create_jsonable_registry(self):
    """Creates a JSON-able representation of this object.

    Returns:
      A dictionary mapping (device, tensor name) to JSON-able object
      representations of NumericsAlertHistory.
    """
    # JSON does not support tuples as keys. Only strings. Therefore, we store
    # the device name, tensor name, and dictionary data within a 3-item list.
    return [HistoryTriplet(pair[0], pair[1], history.create_jsonable_history())
            for (pair, history) in self._data.items()]