Hide Value class constructor

Value class was constructable and it had hidden abstract methods.
This is an issue, Changing to private constructor so that internal
implementors can still call it, but this class can no longer be
implemented by external implementors.

Test: make update-api
Merged-In: Ifb9849e478cff31d0ad2d2fd5d518c207a8764eb
Change-Id: Ifb9849e478cff31d0ad2d2fd5d518c207a8764eb
2 files changed