Make sure to call onTasksAppeared when app transiton is handled.

Bug: 246340474
Test: manual.
   1. start an activity which request permission.
   1. quick switch to other task, and moves back to the previous task
      several times.
   1. check navbar is dispayed and touch works.
Change-Id: Ic698ebd35ac1bf5b4b471c080c11ef571d18a650