function constraintTimingToEnumType(constraintTiming) {
  switch (constraintTiming) {
    case 'deferrable': return lf.ConstraintTiming.DEFERRABLE;
    case 'immediate': return lf.ConstraintTiming.IMMEDIATE;
    default: throw new Error('Invalid constraint timing: ' + constraintTiming);
  }
}
@param {string} constraintTiming
@return {!lf.ConstraintTiming}
@suppress {missingRequire}