LibWeb: Stop traversal early when marking nodes for child style update

These flags always propagate to the root, so once we encounter an
ancestor with the flag set, we can stop traversal since everything above
it will already be set as well.

Userland/Libraries/LibWeb/DOM/Node.cpp

@@ -1174,6 +1174,8 @@ void Node::set_needs_style_update(bool value)
 
     if (m_needs_style_update) {
         for (auto* ancestor = parent_or_shadow_host(); ancestor; ancestor = ancestor->parent_or_shadow_host()) {
+            if (ancestor->m_child_needs_style_update)
+                break;
             ancestor->m_child_needs_style_update = true;
         }
         document().schedule_style_update();