Add a Matrix type and cube gemetry generation helper functions.

BUG=angle:521

Change-Id: Ia50be1790d6f440499eea052f427762637f3c876
Reviewed-on: https://chromium-review.googlesource.com/188727Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>