It was passing the attribute size, not the stride, so it worked only
when they were the same.
Enable corresponding tests.

BUG=angleproject:2310

Change-Id: Ie3ab13567c16c302aa9aeda5d059e5fd4eb92b4e
Reviewed-on: https://chromium-review.googlesource.com/875304
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>