Merge changes I33358ce4,I5746ffae,Ie307ce30,I8cd5eb46,Ie02ddd37, ...

* changes:
  OMS: reduce number of OVERLAY_CHANGED broadcasts
  Revert "Revert "OMS: add transactional API""
  Revert "Revert "Push OverlayDeviceTests onto /system""
  Revert "Revert "OMS: add tests for the OMS transactional API""
  Revert "Revert "OMS: block until settings are persisted""
  Revert "Revert "OMS: replace OMSImpl.OverlayChangeListener with return v...""