Make ValidationUtils flexible for other generation.
BUG=dawn:1201
Change-Id: I42ccbd3d9c2fe37abec4b8f7eb395583dbe1dc8d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/72980
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Junwei Fu <junwei.fu@intel.com>