Previously, TrailerFlags was unreferenced in std,
so its tests were never run.
Also, fix the use of `default_value` whose type was changed in
f4a249325e8e3741a6294462ae37a79cb9089c56 (#10766).
8b8e57c670Erik Arvstedt committed on 5/4/2022, 6:01:48 PMparent3ed9ef3