Make scroll bars more noticeable on round screens.

Increase alpha from 15 to 30% for the track and use Google Material
Grey 200 for the thumb. Fix the geometry so that the track and thumb
don't extend off the edge of the screen.

Bug: 80258942
Change-Id: I43e603e5fffb8a05f486af35194c801060dd0b51
(cherry picked from commit 97b00cbc039a090659aed75e47a172a70222b02f)