I would like to take this issue if no one working on this.

Sure thing. I can review.

jdragon.bae@, please add me into the CC as well.

I'm trying to fix this issue. And I think PlatformScreen should be implemented in ui/ozone/platform/headless/headless_screen.h like Wayland[1], Scenic[2]. 
However, I'm not sure if it's the good start point.
Could you give me some guidance or reference? Thanks :)

[1]https://chromium-review.googlesource.com/c/chromium/src/+/1236268
[2]https://chromium-review.googlesource.com/c/chromium/src/+/1162426



 

yes. There should be a file headless_screen.{h,cc}

You should create a subclass of PlatformScreen and implement its methods, write appropriate unit tests etc. The wayland implementation is a mostly reasonable starting point. 

The PlatformScreen class comments do not provide a great deal of assistance to implementors. It is perhaps desirable to start by expanding that with some comments? That would be a comparatively easy first CL that would require you to understand what a PlatformScreen implementation actually needs to do.