Minimal change to ensure events are propagated to the right DividerView.

- The RecentsDrawnEvent sent when Recents is first drawn can be racey, if
  it is sent before the configuration change in Divider is dispatched, then
  it will be posted for the old DividerView, which prior to ag/2363241 was
  still sending the correct resize calls (the animation is independent of
  the view).  For now, we register the event handler in Divider, and
  instead proxy it to the current view when it is posted.

Bug: 62528361
Test: go/wm-smoke
Test: Play a movie in Play Movies, ensure the activity is resized

Change-Id: I665b0c6af55dea0db1916f5b041589bf72da3baf