Code review comment for lp:~gue5t/midori/restore-middle-btn-up

Does the gtk_widget_get_preferred_height_for_width fail with the Ubuntu global menubar, or with a certain GTK3 theme? I can't seem to reproduce it locally. The assertion sounds like maybe a widget hasn't been realized yet at some point, but it's difficult to figure out realization ordering issues just by looking at code.