Add GLSL output of switch and case BUG=angle:921 Change-Id: I0d752440ce6ffdfcc005f1a6123694bdfeb1b067 Reviewed-on: https://chromium-review.googlesource.com/251526 Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Zhenyao Mo <zmo@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>