Fixed many tests that had empty structures.
Change-Id: Id91312afa39a6293426f99d0dd12578dba46aa61
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/56621
Auto-Submit: James Price <jrprice@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>