Factor GL extension parsing in renderergl_utils.cpp DisplayGLX will use it for the GLX extensions too. BUG=angleproject:892 Change-Id: I5e4f80776a558fcdcc7e7b83767145112bcfee98 Reviewed-on: https://chromium-review.googlesource.com/269461 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org>