Only set ready early in AR.finish if it is a self-contained op

Otherwise, it will cause early-ready during, eg, clearTop
launches which can lead to flickers.

Bug: 273206473
Test: Launch messages, go home, launch phone, pick a contact, then
      pick "text". Observe, no black-flash.
Change-Id: I1badf42914514f3922bc3f6ef67eaa7f10711c84