(It's not called MatrixMode because that collides with the MatrixMode
entry point name)

BUG=angleproject:2306

Change-Id: I9a192701f6248f1e7d4f202c7d1ddfcdbe1b0089
Reviewed-on: https://chromium-review.googlesource.com/990585
Commit-Queue: Lingfeng Yang <lfy@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>