ComboBoxMenuItems use ClutterClones to reconstruct the active item
in the associated ComboMenu to not impose a particular MenuItem type
in the menu. However, this results in style changes (for instance
those triggered by icon-theme or text-scaling-factor changes) of
the ComboBoxMenuItem not having a visual effect until the ComboBoxMenu
is shown.
As a fix, force a style update on the ComboBoxMenu when the item's
style changes.
https://bugzilla.gnome.org/show_bug.cgi?id=662799
d20e646ed6