On GLX, we can expose the EGL_CHROMIUM_sync_control extension by
forwarding to GLX_OML_sync_control when it's available. This will help
with accurate vsync times for Chrome

Bug: 1020252
Change-Id: I9b1e8cf0f8b1a548cc7cc7202fac2d0cdb01d74d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1918104
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>