bug#52885: 28.0.50; xwidget webkit scrolling behaviour confusing or broken with multiple windows

[akira]

On emacs -Q compiled --with-webkit in xwayland on GNOME
- M-x xwidget-webkit-browse-url RET then enter in some url
There are two scroll bars, one for webkit and one for the buffer, the
one for the buffer does nothing. Now

- C-x 3
- C-u N C-x { where N is enough so the window is narrower than the
  webpage

It is now impossible to scroll horizontally in this window to view the
whole webpage (there is no horizontal scroll bar and C-f doesn't work).