user-defined tuple struct could be used to improve type safety.
TEST=cargo test
BUG=None
Change-Id: I8ce10fc51b79c277ab23029513b707f3dd621af5
Reviewed-on: https://chromium-review.googlesource.com/1546432
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: David Tolnay <dtolnay@chromium.org>