bug#16284: 24.3.50; blank column shown with scroll bar configuration changes

[martin rudalics]

> 1. $ emacs -Q -D &

Is "-D &" necessary?

> 2. M-x scroll-bar-mode RET
> 3. M-x scroll-bar-mode RET
>
> Then you'll see a blank column to the right of the scroll bar.

Does the frame shrink after step 2 and expand after step 3?  Does the
blank column appear below the tool-/menubar or at the right of its end?

I suppose everything happens within ns_set_vertical_scroll_bar.  So to
investigate this further, could you please step through this function in
order to find out what's different between when Emacs displays the
scrollbar for the first time and when it executes step 3.  In particular
the respective values of `left' after

  left = WINDOW_SCROLL_BAR_AREA_X (window);

would be interesting.

martin