change scrollbar's width to 6

tower: https://tower.im/projects/d4e0ff64158645f28d99a9ca72d0c27b/todos/d58f53686c784802b8a1a56e839d97bc/

Change-Id: I02c45a1b2225cc745c0cf41fc9d48ad2a7b32743
Merge "change scrollbar's width to 6"