We need the functionality of this extension to support dEQP. Likely
we only needed the minor version enum to not generate an error, but
we can take the time to implement the few cases for the other enums
as well.

We don't support any debug context functionality currently, but we
may want to support it in the future.

BUG=angle:501

Change-Id: Ib74cd2e4581e054f8153bb358824d9296b9f8a1c
Reviewed-on: https://chromium-review.googlesource.com/238083Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>