Version: 56
OS: All

What steps will reproduce the problem?
(1) Add window.onbeforeinstallprompt = <function>
(2) Set up as a PWA (manifest, etc).
(3) Visit site.

What is the expected output?
window.onbeforeinstallprompt is called when Chrome tries to prompt to install.

What do you see instead?
It is ignored.

Note: You can use window.addEventListener('beforeinstallprompt') for this purpose, but the attribute version (window.onbeforeinstallprompt) doesn't work. This was intentional but it looks like the upcoming spec for beforeinstallprompt is going to require this.