Cap user-visible cache size at quota.

Anything over the quota is considered free for storage purposes because
the system can clear it out at will. This is reflected in the top level
Storage Settings, but not in the ApplicationsState-based views. This
change makes ApplicationsState cap the cache size as well.

Change-Id: I733a39da7fea993065d767978b4191cc82f908b8
Fixes: 65384688
Test: b/34768986