Scroll: modified velocitytracker

Velocitytracker and overscroll are called on every touch event to
calculate if there is a scrolling/fling. Move this and the recycling
to static voids so they are pre-optimized at compile time rather than
after evoking the method call during runtime (JIT) to increase responsiveness.

-Vanir

Change-Id: Ic7351da58f29281ca2b6a788386b95b68b552390