UserAgent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.36

Steps to reproduce the problem:
1. Enable the 'Generic Sensor', 'Generic Sensor Extra Classes' and 'Experimental Web Platform features' in chrome://flags.
2. Debug in console on Dev tools as below:
  let a = new Accelerometer({frequency: undefined});
  let ar = new Accelerometer({referenceFrame: undefined});

What is the expected behavior?
TypeError should be thrown when value of SensorOptions is undefined 

What went wrong?
No error throw.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 67.0.3397.0  Channel: canary
OS Version: 10.0
Flash Version: 

Also reproduce in case link: https://w3c-test.org/accelerometer/Accelerometer.https.html

Test Name: 
Accelerometer: throw 'TypeError' if frequency is invalid
Accelerometer: throw 'TypeError' if referenceFrame is not one of enumeration values