UserAgent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:57.0) Gecko/20100101 Firefox/57.0

Steps to reproduce the problem:
1. Run google-chrome-unstable --user-data-dir="/tmp/chrometestdata" --unsafely-treat-insecure-origin-as-secure="http://my.example.dev" --ignore-certificate-errors
2. Visit http://my.example.dev
3. Open Developer tools > Application > Manifest 
4. Click Add to homescreen

What is the expected behavior?
The browser should show a panel, with the following text: "Add this site to your shelf to use it anytime" and a confirm button. This works, when I visit http://localhost, but I need to use a custom domain name.

What went wrong?
After clicking on the 'Add to home screen' link, I get an error message: 'Site cannot be installed: the page is not served from a secure origin'

Did this work before? N/A 

Chrome version: <Copy from: 'about:version'>  Channel: dev
OS Version: Version 65.0.3298.3 (Official Build) dev (64-bit)
Flash Version: 

The flag --unsafely-treat-insecure-origin-as-secure works correctly because without it I am unable to register the Service Worker. It seems that the feature 'Add to home screen' ignores the flag --unsafely-treat-insecure-origin-as-secure. Everything works with the localhost domain and the same code.