GLX backend: fallback to lesser swap_control extensions We would like to use the EXT_swap_control extension to specify the swap interval of each drawable independently. However open source drivers do not expose this extension and instead expose the MESA and SGI versions that have a global swap interval. This commit changes the code to use the best swap_control extension it can, potentially changing the swap interval on each swap buffers on lesser extensions. BUG=angleproject:1206 Change-Id: I48e40e443ff9a258fc33b38efb0acf6b1f3db103 Reviewed-on: https://chromium-review.googlesource.com/311244 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org>