Fix split view crashes when using keyboard navigation with some themes
The current code uses hard-coded values for some theme items. This
fix uses the scrollbar width. There are other theme issues with split
views.
Test using Oxygen application style (+ increase scrollbar width)
Most patch by Nikolay Zlatev <nik@astrapaging.com>
BUG: 411387
cherry-picked from 63ef8872bfc485248a8de6c7b45909afc68bfcc9