Cache the hash of the test output, and only re-validate if the output changes.
This speeds up incremental end-to-end testing.
Change-Id: I44bc1eff62320df1e80524e8481d1c012fb67f42
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/109761
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Auto-Submit: Ben Clayton <bclayton@google.com>