We can't assume we have a simple mapping between input attribs
and shader attribs. The app specifies matrix input attribs as
several vector inputs, while the shader uses a single matrix type.

BUG=angle:576

Change-Id: I4e3cdde4a14a5f06b86052dfe0325113cbe8e599
Reviewed-on: https://chromium-review.googlesource.com/189193Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>