[Nouveau] Chromium - Application-level nouveau blacklist

It looks like as of Chromium 71, nouveau is completely blacklisted. I don't really see a way back from this, since they don't cite any easily reproducible issues, except that some people had some issues with indeterminate hardware and indeterminate versions of mesa. In the bug that triggered this (https://bugs.chromium.org/p/chromium/issues/detail?id=876523), where I might have slightly lost my cool, they (at the end) suggested that we try to make nouveau a first-class citizen with chromium. However I will never be able to present concrete evidence that inconcrete issues are resolved. I did run the WebGL CTS suite, but that resulted in some hangs from the the max-texture-size-equivalent test, and some browser-level weirdness after some tests where later tests all fail (due to what I have to assume is a browser bug). I don't think I managed to properly track down the true reason why. I didn't want to reach out to them with such results, as that's just further evidence of nouveau not working perfectly. In the meanwhile, end users are losing accelerated WebGL which in practice worked just fine (at least in my usage of it), and probably some other functionality. One idea is to flip GL_VENDOR to some random string if chromium is running. I don't like this idea, but I also don't have any great alternatives. We can also just take this, as yet-another nail in the nouveau coffin. Opinions welcome. Cheers, -ilia