Fix some wrong-thread issues around animator management

 Bug: 17372309

 Fixes a case where UI thread and RT thread both used the same method
 which wasn't safe for either of them.

 Adds additional assertions & logging in unusual circumstances to
 try and track down where the issue is occuring from.

Change-Id: I93d31a6fd0c5927259b67bdf96a475944226eee6