This removes blocks of code that were obviously builder-specific but
also removes the ObjectStorage::valid member that was used to implement
the maybe monad on the wire server side. This is no longer needed since
dawn_native handles the maybe monad internally now.
BUG=dawn:125
Change-Id: I8c30daae9fc70853bc1996d85a860b4877c5976c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/6161
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>