When a horizontal scrollbar is added to the TTV,
the grey bar to the right of the scrollbar has no
border line along its top, and so looks a little
bit incomplete, especially since the scrollbar
seems to have a border along its top.
This issue blocks the umbrella issue 33281 - TreeTableView improving. All TTV's
issues should be fixed separately at once on base UI spec (task 31621).
Horizontal scrollbar will be removed in TTV rewrite - it was a horrendous idea which
causes a number of the horrific bugs. Components are resizable and so are columns.
Also, since L&Fs other than metal use bitmaps for their scroll buttons, and metal is no
longer the default L&F, this isn't terribly relevant.