Add abstract control class.

Partial implementation of tagged_partial_metadata. A control
is a value that can be changed.
Implements supported/get/set of parent class, abstracting
into simpler supported/get/set methods for children to implement.

BUG: 30140438
Change-Id: Iaba6fc2f54f6a8786c5ca379972ee1da9604c7a3
TEST: unit tests pass
4 files changed
tree: 6910f4085538ebb37f8f68bfa7bd41aea537b0c4
  1. modules/