The GL spec states that by default a vertex attribute has a size of 4.

Change-Id: Ic4c977fb936cc0b232ed4742eeb061d6ba6843be
Reviewed-on: https://chromium-review.googlesource.com/181522Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>