UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.87 Safari/537.36

Steps to reproduce the problem:
1. Open https://jsfiddle.net/Lj2fs5kr/ in regular mode & incognito mode
2. 
3. 

What is the expected behavior?

What went wrong?
It shows "false" in regular mode and "true" in incognito mode. This allows the site to detect if the user uses the private mode and hide some content from them to discourage using this mode. I think the browser should hide such details so that sites are not able to apply such detection.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 56.0.2914.0  Channel: canary
OS Version: OS X 10.12.1
Flash Version: Shockwave Flash 23.0 r0