bug 1303964 draw only background and frame of separator menuitems in …

…GTK versions > 3.20 r=stransky+263117

In GTK 3.20, gtk_menu_item_draw() just draws the root widget gadget, depending
on the theme to style menu items with CSS name "separator" appropriately.

MozReview-Commit-ID: 6AIxPzFe0Rg

--HG--
extra : rebase_source : 58a1ab4c78d94cf186e923354332ecb30aa491f8

widget/gtk/gtk3drawing.cpp

@@ -1774,6 +1774,9 @@ moz_gtk_menu_separator_paint(cairo_t *cr, GdkRectangle* rect,
     moz_gtk_menu_item_paint(MOZ_GTK_MENUSEPARATOR, cr, rect,
                             &defaultState, direction);
 
+    if (gtk_get_minor_version() >= 20)
+        return MOZ_GTK_SUCCESS;
+
     GtkStyleContext* style;
     gboolean wide_separators;
     gint separator_height;