function getDirections_(origin, destination) {
  const directionFinder = Maps.newDirectionFinder();
  directionFinder.setOrigin(origin);
  directionFinder.setDestination(destination);
  const directions = directionFinder.getDirections();
  if (directions.status !== 'OK') {
    throw directions.error_message;
  }
  return directions;
}
A shared helper function used to obtain the full set of directions
information between two addresses. Uses the Apps Script Maps Service.

@param {String} origin The starting address.
@param {String} destination The ending address.
@return {Object} The directions response object.