Legacy setting syncer.

We need to respect the user's settings when we update quick affordance
selections and vice versa. See the documentation of the class for more
details.

Fix: 256662760
Test: added unit tests. Manually verified that updating settings and
selections updates the other side as expected.

Change-Id: Icd8ff1558fe887ca765ce325b97e7815f124b0db
8 files changed