This fixes some broken tests in dEQP:
functional.shaders.conversions.matrix_to_matrix

BUG=angle:712

Change-Id: I0538595f2913a2c1d4f0da901d65d608a6580d19
Reviewed-on: https://chromium-review.googlesource.com/210882Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>