Fixing regression in animation of drag task.

- Should be ignoring the drag task, caused by a bad merge in ag/854463.
- Preventing relayout when picking up a new task view.  This issue
  caused the task view to be relaid out mid-drag if the animation in the
  stack causes a new TaskView to be picked up from the pool (ie. when
  dragging immediately after starting recents from scratch)

Change-Id: Id798cc39216d7ccbaa106c687aa0a518e7d5155f