Optimize gtk_css_node_declaration_has_class

This function is getting called a lot. Statistics for the gtk3-demo
listbox example show most calls with 0-4 classes. Unrolling the cases
a bit brings the instruction count in callgrind from 93M to 52M.

gtk/gtkcssnodedeclaration.c

@@ -311,8 +311,29 @@ gboolean
 gtk_css_node_declaration_has_class (const GtkCssNodeDeclaration *decl,
                                     GQuark                       class_quark)
 {
+  GQuark *classes = get_classes (decl);
+
+  switch (decl->n_classes)
+    {
+    case 3:
+      if (classes[2] == class_quark)
+        return TRUE;
+
+    case 2:
+      if (classes[1] == class_quark)
+        return TRUE;
+
+    case 1:
+      if (classes[0] == class_quark)
+        return TRUE;
+
+    case 0:
+      return FALSE;
+
+    default:
       return find_class (decl, class_quark, NULL);
     }
+}
 
 GList *
 gtk_css_node_declaration_list_classes (const GtkCssNodeDeclaration *decl)