Description:
Linux-based ChromeOS officially supports VA-API and recently Chromium has made some progress with integrating it, but until now it is officially not supported.

Meanwhile Daniel Charles (Intel) created two new feature flags accessible via chrome:flags to enable hardware acceleration on Linux [1]. Although this change has not been merged into the code base, it works quite well and has undergone some testing by the Arch Linux community at [2].
Until now these changes were rebased with each new Chromium release and hopefully they will be accepted someday.

Should hardware acceleration not be available for whatever reason, then Chromium falls back to software decoding and plays the video nevertheless.

Before VA-API can be used, the user needs to manually enable the features 'Hardware-accelerated video' and 'Hardware-accelerated mjpeg decode for captured frame' at chrome:flags.

The only downside I see to this is the maintenance of an additional patch.

Necessary changes:
- 'libva' library present at compile time
- adjusted library paths due to recent upgrade to libva 2.0 [3]
- VA-API patch [4]
- 'use_vaapi=true' in _flags array

Verifying acceleration:
Play a video and check if 'chrome:media-internals -> Player Properties -> video_decoder' shows GpuVideoDecoder.

Steps to reproduce:
See chromium-vaapi in the AUR. [2]

1: https://chromium-review.googlesource.com/c/chromium/src/+/532294
2: https://aur.archlinux.org/packages/chromium-vaapi/
3: https://aur.archlinux.org/cgit/aur.git/tree/chromium-libva-r2.patch?h=chromium-vaapi
4: https://aur.archlinux.org/cgit/aur.git/tree/chromium-vaapi-r15.patch?h=chromium-vaapi