Will be tested in Chromium's webgpu_mailbox_unittest.cc
Bug: chromium:1359106
Change-Id: I8a9bf01cd593f2835e2876fa04139fd3afda9b2e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/103462
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>