To Reproduce
Steps to reproduce the behavior:

1. Use wf-panel
2. Use one panel on bottom of screen with several widgets including a window list,
3. Create lots of windows, such that the window list width is constrained by available panel width

Expected behavior
Windows icons in list get smaller and CPU usage stays low.

Actual behaviour
wf-panel starts consuming 100% of one CPU. WayfireWindowList::on_draw continuously runs this code - maybe once every frame?

    /* We have changed the size/number of toplevels. On top of that, our list
     * is longer that the max size, so we need to re-layout the buttons */
    if (preferred_width > allocated_width && toplevels.size() > 0)
        set_button_width(get_target_button_width());

Wayfire version
0.7.4-2 from debian testing

Panel configuration

widgets_left = menu launchers spacing4 window-list
widgets_center = none
widgets_right = volume network battery clock
# ... configuration for 6 launchers
launchers_spacing = 0
launchers_size = 34