Test the emulated GLSL functions against multiple GL versions.

BUG=angleproject:1044

Change-Id: I1e12523301042f0d541ab2f4e73f02319d1584ef
Reviewed-on: https://chromium-review.googlesource.com/277702Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>