FunctionsGLX: add glXGetCurrent(Drawable|Context) support BUG=angleproject:1188 Change-Id: Ibf0fb4be3ec08cc43b2d9aba03a3d0fc12adce9d Reviewed-on: https://chromium-review.googlesource.com/309140 Tryjob-Request: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org>