LibWeb: Give DOM::Node a direct pointer to its Paintable

Instead of going via the layout tree.

Userland/Libraries/LibWeb/DOM/Node.cpp

@@ -41,6 +41,7 @@
 #include <LibWeb/Layout/Node.h>
 #include <LibWeb/Layout/TextNode.h>
 #include <LibWeb/Layout/Viewport.h>
+#include <LibWeb/Painting/Paintable.h>
 
 namespace Web::DOM {
 
@@ -103,6 +104,7 @@ void Node::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_child_nodes);
 
     visitor.visit(m_layout_node);
+    visitor.visit(m_paintable);
 
     for (auto& registered_observer : m_registered_observer_list)
         visitor.visit(registered_observer);
@@ -1438,18 +1440,19 @@ size_t Node::length() const
     return child_count();
 }
 
+void Node::set_paintable(JS::GCPtr<Painting::Paintable> paintable)
+{
+    m_paintable = paintable;
+}
+
 Painting::Paintable const* Node::paintable() const
 {
-    if (!layout_node())
-        return nullptr;
-    return layout_node()->paintable();
+    return m_paintable;
 }
 
 Painting::Paintable* Node::paintable()
 {
-    if (!layout_node())
-        return nullptr;
-    return layout_node()->paintable();
+    return m_paintable;
 }
 
 Painting::PaintableBox const* Node::paintable_box() const

Userland/Libraries/LibWeb/DOM/Node.h

@@ -187,6 +187,8 @@ public:
     Painting::Paintable const* paintable() const;
     Painting::Paintable* paintable();
 
+    void set_paintable(JS::GCPtr<Painting::Paintable>);
+
     void set_layout_node(Badge<Layout::Node>, JS::NonnullGCPtr<Layout::Node>);
     void detach_layout_node(Badge<Layout::TreeBuilder>);
 
@@ -671,6 +673,7 @@ protected:
 
     JS::GCPtr<Document> m_document;
     JS::GCPtr<Layout::Node> m_layout_node;
+    JS::GCPtr<Painting::Paintable> m_paintable;
     NodeType m_type { NodeType::INVALID };
     bool m_needs_style_update { false };
     bool m_child_needs_style_update { false };

Userland/Libraries/LibWeb/Layout/LayoutState.cpp

@@ -209,6 +209,8 @@ static void build_paint_tree(Node& node, Painting::Paintable* parent_paintable =
         parent_paintable->append_child(paintable);
     }
     paintable.set_dom_node(node.dom_node());
+    if (node.dom_node())
+        node.dom_node()->set_paintable(&paintable);
     for (auto* child = node.first_child(); child; child = child->next_sibling()) {
         build_paint_tree(*child, &paintable);
     }