Move the common validation code to a shared base function.

BUG=angle:571

Change-Id: Id70b413b408a21f0a8933cfd4a09e261e637bae1
Reviewed-on: https://chromium-review.googlesource.com/200559Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>