GLES1: glClientActiveTexture + adds query for GL_MAX_TEXTURE_UNITS BUG=angleproject:2306 Change-Id: Ie89fa6a067551170856bf0f7e6d7b4452b3da132 Reviewed-on: https://chromium-review.googlesource.com/984894 Commit-Queue: Lingfeng Yang <lfy@google.com> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>