setExtraDisableReasonFinder(customDisableReasonFinder) {
        this.gate.customDisableReasonFinder = customDisableReasonFinder;
        return this;
    }
Specifies a function for retrieving unusual reasons a gate is being misused and so must be disabled.
@param {!function(!GateCheckArgs) : (undefined|!string)} customDisableReasonFinder
@returns {!GateBuilder}