Also implements and tests validation / negative API.

Bug: angleproject:3944
Change-Id: I3385a4255f4fab6a12eee2abfa5ffcce2107359a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1879961
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>