Move them to the constructor
Bug: tint:390
Change-Id: I30bb6a1de060b790bf5202194d020d4e3889a307
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/35008
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>