GL: Put commas between vendor and renderer strings. This allows ANGLE's GL backend's renderer string to be parseable. BUG=882580 Change-Id: I834dc236b1b72edcbc5285bcca4a1962f95f490d Reviewed-on: https://chromium-review.googlesource.com/c/1337463 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>