This patch also incidentally fixes some bugged validation in the
new ES3 unsigned int uniform API entry points.

BUG=angle:571

Change-Id: I89bd909467bd9418fe5ce3f246561765cf27a5e9
Reviewed-on: https://chromium-review.googlesource.com/200074Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>