bug 1272194 only add menubar class to menu items with GTK 3.4 r=stransky+263117

and save/restore context consistent with GTK 3.4.

MozReview-Commit-ID: GdMoAmzOJlf

--HG--
extra : rebase_source : c3cb854a304a0bc10cd27325b42361031a5107db

widget/gtk/gtk3drawing.cpp

@@ -2473,8 +2473,15 @@ moz_gtk_menu_item_paint(WidgetNodeType widget, cairo_t *cr, GdkRectangle* rect,
         }
         style = gtk_widget_get_style_context(item_widget);
 
-        if (widget == MOZ_GTK_MENUBARITEM) {
-            gtk_style_context_add_class(style, GTK_STYLE_CLASS_MENUBAR);
+        bool pre_3_6 = gtk_check_version(3, 6, 0) != nullptr;
+        if (pre_3_6) {
+            // GTK+ 3.4 saves the style context and adds the menubar class to
+            // menubar children, but does each of these only when drawing, not
+            // during layout.
+            gtk_style_context_save(style);
+            if (widget == MOZ_GTK_MENUBARITEM) {
+                gtk_style_context_add_class(style, GTK_STYLE_CLASS_MENUBAR);
+            }
         }
 
         gtk_widget_set_direction(item_widget, direction);
@@ -2490,8 +2497,8 @@ moz_gtk_menu_item_paint(WidgetNodeType widget, cairo_t *cr, GdkRectangle* rect,
         gtk_render_background(style, cr, x, y, w, h);
         gtk_render_frame(style, cr, x, y, w, h);
 
-        if (widget == MOZ_GTK_MENUBARITEM) {
-            gtk_style_context_remove_class(style, GTK_STYLE_CLASS_MENUBAR);
+        if (pre_3_6) {
+            gtk_style_context_restore(style);
         }
         gtk_style_context_set_state(style, GTK_STATE_FLAG_NORMAL);
     }