This is X-related part of CR 6353378 with some additional misbehavior spotted.

=== Test program ...

... is attached. It creates Frame with MenuBar and 7 buttons.
A click on "popup" will show a popup menu.
"root-font-..." buttons will set both MenuBar and PopupMenu font to null, big, or small font accordingly, when a mouse is over them.
"m1_-font-..." buttons will set font the same way, but only for "..._1_" menu item (also both in MenuBar and PopupMenu).

To reproduce misbehaviours you should open nested submenu windows, hover your mouse over "...-font-..." buttons, and look at what happens.

=== Misbehaviors (all) are:

1. If font is changed for "root" menu (MenuBar or PopupMenu), then menu cells sizes are not recalculated.

2. Consider the case, if menu bar size changes (if a bigger or lesser font is set for all or one of its items). Then its parent Frame client area size changes, but currrently Frame doesn't react to this resize, and its contents are not re-layout.