Chrome Version: 65.0.3325.162
OS: OSX

What steps will reproduce the problem?
(1) Start chrome with --unsafely-treat-insecure-origin-as-secure and --user-data-dir flags
(2) Load http page with a manifest on the domained passed in with the flag
(3) In Dev Tools > Application click Add to homescreen

What is the expected result?
App installs successfully

What happens instead?
I get the error message in the console "Site cannot be installed: the page is not served from a secure origin"