It's not an attack. Each platform's methods of GPU IPC are pretty sparsely documented. Two months ago I wouldn't have known about them; I only learned by working on integrating Chromium's sandbox into an application that needed to work with the GPU within a sandboxed process.

That doesn't change the fact that none of the things you listed are unsupported by Chrome's sandbox model, and if you only need to establish a barrier around the video pipeline (and not e.g. VLC's ability to notice device status or interact with webcams) you don't even need 3/4 of what Chromium's sandbox has implemented. Like I said, I've actually walked the walk when it comes to using their sandbox for Windows and Linux with a process that needed to access certain user files, the GPU, and even each platform's font server equivalent, so this isn't me just spitballing about some theoretical solution.