I presume that we need this on CrOS as well? Or is there a separate bug for that?

Do you mean  crbug.com/581463 ? I would say this is a separate task, despite there being lots of overlap, since having overlays working on CrOS isn't required to launch on Windows.

I need to look into if overlays were ever enabled on Windows.

It looks like we can use overlays on Windows for video. There is more information in crbug.com/678800.  Although, the HP Z840 I was testing on doesn't have overlay support.

You need modern Intel integrated GPUs afaik. 

+zmo,sunnyps,vmiura

How important is Windows overlay support? Can we run a limited finch trial without it essentially?

If it is essential, is this a task that someone in MTV could complete in the next ~2 weeks or should I start looking into it?

We definitely need overlay support for videos at least, and maybe more in the future.

Per offline discussion, kylechar will take a look at the scope of this task, and will either upload a CL (if it's trivia) or hand over to sunnyps@ or me (if it's relatively larger scale and requires more study)

Assigning to kylechar@ for now

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d4022a6e7035ea5e1cc68c81be4209b473790548

commit d4022a6e7035ea5e1cc68c81be4209b473790548
Author: kylechar <kylechar@chromium.org>
Date: Thu Feb 15 19:08:59 2018

Support Windows overlays with VizDisplayCompositor.

Add an OutputSurface for Windows that supports overlays when running
with --enable-features=VizDisplayCompositor. The OutputSurface just
needs to provide a CompositorOverlayCandidateValidatorWin.

Bug:  787486 
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I01cf5baea5298386e53d831d0674bde79d1fce28
Reviewed-on: https://chromium-review.googlesource.com/921661
Commit-Queue: kylechar <kylechar@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537090}
[modify] https://crrev.com/d4022a6e7035ea5e1cc68c81be4209b473790548/components/viz/service/BUILD.gn
[add] https://crrev.com/d4022a6e7035ea5e1cc68c81be4209b473790548/components/viz/service/display_embedder/gl_output_surface_win.cc
[add] https://crrev.com/d4022a6e7035ea5e1cc68c81be4209b473790548/components/viz/service/display_embedder/gl_output_surface_win.h
[modify] https://crrev.com/d4022a6e7035ea5e1cc68c81be4209b473790548/components/viz/service/display_embedder/gpu_display_provider.cc

I'm like 95% sure that this is fixed. I haven't actually found a Windows machine that supports overlays to test it out though, so I can't verify it's actually working.

sunnyps tested this and it works.