Fixing issue where affiliated task last-active-times were inconsistent.

- We rely on the last-active-times of the task records to order tasks
  in Recents, but for affiliated tasks, their last-active-time was never
  set until the task was launched.  This change just ensures that all
  tasks have a valid last-active-time, and for affiliated tasks, ensures
  that the task that they were launched behind always has a later
  last-active-time.

Bug: 27597746
Change-Id: I9692c2b48ac6d12266de90bdf423f689402a94c2