Allow overlays to be notified about theme changes

Overlays should override onOverlaysApplied() in order to act upon theme
changes.

Test: manual
Bug: 190093578
Change-Id: Ie52b8c55a046d150dd30aae5fabb279b53a959f5
Merged-In:Ie52b8c55a046d150dd30aae5fabb279b53a959f5
3 files changed