I would like to get ChromiumOS running on Virtualbox again, which it was for a while but is no longer since they switched away from using X to DRM + KMS.
The first thing I want to try is just building a suitable kernel module for vboxvideo and including it in a custom chromium os image that I build.
It doesn't appear that the guest additions are intended to be used in this way. Note that chromium OS devices do not have build utils and the current status of ChromiumOS is "won't even boot in virtualbox".
I would like to build a version of the guest utils (or at least the vboxvideo module) for the 4.4 kernel used by the amd64-generic overlay. Any thoughts about how I can convince the guest utils to do this?