Some windows are not shown in window chooser

[Ashark]

I have noticed, that some windows are invisible in window chooser in Hangouts.
For example Krita window.

Steps to reproduce:

1. Start a video call at https://hangouts.google.com/. It is possible to just make a dummy hangouts call to not bother your friends. So you can just press video camera button that is in middle of the screen.
2. Launch krita application.
3. In hangouts chromium window go to upper menu (three dots icon) -> Share screen -> Application window tab.
4. You can see that there is no krita window there.

Versions:

archlinux 4.16.6-1-ARCH
krita 4.0.2
Chromium 66.0.3359.139 Arch Linux
KDE Plasma 5.12.5
KDE Frameworks 5.45.0
Qt 5.10.1

We should explore why this is happening.
Actually this should go to chromium bugtracker, but I will left it here.