@jumpsq said:
Yes, that would certainly be nice, but I'd assume that such a feature would have to be implemented for Gnome, KDE, XFCE, Unity, [i3, awesome, sway] ... each (or is there some common API that all these Desktop Environments/Window Managers use?).
I searched on this topic a bit and found out that X apps should be able to use _NET_WM_XAPP_PROGRESS window property (I found this only for Cinnamon, but to me this seems universal enough that also other DEs (in fact, panels) should support it). About Wayland (and others) we don't have to care for now, because Chromium is X-only now AFAIK.