Certain vertex formats using fewer than 4 bytes could confuse our
buffer code, giving us improperly aligned offsets. Aligning vertex
data across the board should fix the problem, and minimal cost.

Change-Id: I6884b4ddcfb91ef309a970593aaf7932cb65712e
Reviewed-on: https://chromium-review.googlesource.com/185196Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>