bug#31546: 27.0.50; macOS child frames with no mode-line mouse click problem

[Eli Zaretskii]

> From: Aaron Jensen <aaronjensen@gmail.com>
> Date: Thu, 24 May 2018 03:53:54 -0700
> Cc: 31546@debbugs.gnu.org, Alan Third <alan@idiocy.org>
> 
> The window selected in posn-set-point is the window in the child frame,
> which is the window that scrolls (and that I do not want to scroll).
> 
> But, the thing doing the scrolling is 'mouse-drag-region', which calls
> 'mouse-drag-track', which calculates the bottom of the window incorrectly
> if it does not have a mode-line.

Is this NS specific?  I cannot reproduce any problem with the original
recipe posted with this bug report, but maybe you are already using a
modified one (the talk about pixelwise resizing seems to suggest
that)?

If it's NS-specific, I'd like to understand the issue deeper before we
decide how and on which branch to fix it.

Thanks.