[ActivityManager] Fix activity always visible.

Sample code, symptom video and detail:
http://code.google.com/p/android/issues/detail?id=87909

If the activity state was stopping or later state,
it should not apply paused flow again.

Issue flow:
1.At home stack and screen off.
2.A task T contains one activity Z and its process was died.
3.Launch new activity X on T.
4.Before activity Z complete resume, any process
  bound and died trigger update visibility and resume top.
5.X calls finish.
6.Turn on screen, X will be always visible.

Change-Id: I8ca1845fd100e13ec58382c8c0105bf0a9f8137d