DisplayGLX will use it for the GLX extensions too.

BUG=angleproject:892

Change-Id: I5e4f80776a558fcdcc7e7b83767145112bcfee98
Reviewed-on: https://chromium-review.googlesource.com/269461Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>