GLES1: Shade model API + add sample BUG=angleproject:2306 Change-Id: Ie0c391618ec2b771cc99b96db02b9008a86272b9 Reviewed-on: https://chromium-review.googlesource.com/1079992 Commit-Queue: Lingfeng Yang <lfy@google.com> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>