Use gtk_widget_get_preferred_size with GTK3
Use primary-toolbar style in GTK3
toolbar-editor: Fix dragging items out of the toolbar

When 'window-dragging' is True, GtkToolbar starts a drag in the
'button-press-event'. By connecting a callback to 'button-press-event'
after setting gtk_drag_source_set that return TRUE we prevent
GtkToolbar handler to be called.

https://git.gnome.org/browse/evince/commit/?h=gnome-3-0&id=c48141968a2b374fe7a666feaf2635a82a528dac