As pointed out in review, if the current time is after the end of the
slider, the correct hit object to use for sample retrieval is the object
itself, not any nested object.
- It is entirely derived from `SkinLayoutInfo.DrawableInfo`, which is
the actual primary thing we want to serialise.
- It will never get read out from any serialised files anyway (corollary
of the previous point - it is a get-only property derived from another).
- It is only used in tests.
All of the three reasons above make serialising the property out to skin
files nothing more than a waste of space.