Add a GLES3 GoogleTest target. BUG=510822 BUG=angleproject:1071 Change-Id: Ia2e6d0ac71e61dbed75e55994d2bf874a75fabd6 Reviewed-on: https://chromium-review.googlesource.com/286831 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Kenneth Russell <kbr@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>