ExpandHelper: Performance improvement during expanding

- Reflects on Hover mainly
- Add an helper to get natural height

Thanks to Kiril Mikos @mik9 http://review.cyanogenmod.org/#/c/66676/

Change-Id: Ib125d77e03c244879bf244c5abbb23582ad94115
Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>