Ensure frame callback applied during scroll handling is applied.

- By the time we call computeScroll(), the current frame's callback
  has already been consumed, which makes it impossible to apply
  surface updates with the current frame (in response to the scroll).
  Instead, we should only consume the frame callback after dispatching
  draw for the current frame (but before the window callbacks which
  may reset the frame callback).

Test: Update surface transforms in response to scroll, ensure that
      it is updated with the current frame

Change-Id: I52a640604ee15cf745c47fc0120b4844b67f35be