The only way to get a core profile context of the highest version using
CreateContextAttrib is to try creationg contexts in decreasing version
numbers. It might look that asking for a core context of version (0, 0)
works on some driver but it create a _compatibility_ context of the highest
version instead which might not be supported on some drivers.

BUG=angleproject:1994

Change-Id: Ic8a33243909c54ea5940ee81c9c866b141bea420
Reviewed-on: https://chromium-review.googlesource.com/480739
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>