```
// We guarantee our robustness via these requirements:
// * Object.MutTiedFields() gives us a tuple,
// * where the combined sizeofs all field types sums to sizeof(Object),
// * (thus we know we are exhaustively listing all fields)
// * where feeding each field back into ParamTraits succeeds,
// * and ParamTraits is only automated for BytesAlwaysValidT<T> types.
// (BytesAlwaysValidT rejects bool and enum types, and only accepts int/float
// types, or array or std::arrays of such types)
// (Yes, bit-field fields are rejected by MutTiedFields too)
```
BytesAlwaysValidT<T> is the same as the IsTriviallySerializable<T> that
it replaces, however the emphasis is different, and should discourage
tagging structs as IsTriviallySerializable, since they more clearly
aren't BytesAlwaysValid.
Differential Revision: https://phabricator.services.mozilla.com/D151676
Kelsey Gilbert