LibHTML: Create some subdirectories.

LibHTML/Layout/LayoutNode.h

@@ -0,0 +1,54 @@
+#pragma once
+
+#include <AK/Retained.h>
+#include <AK/Vector.h>
+
+class Node;
+
+class LayoutNode {
+public:
+    virtual ~LayoutNode();
+
+    void retain();
+    void release();
+    int retain_count() const { return m_retain_count; }
+
+    const Node* node() const { return m_node; }
+
+    LayoutNode* next_sibling() { return m_next_sibling; }
+    LayoutNode* previous_sibling() { return m_previous_sibling; }
+    LayoutNode* first_child() { return m_first_child; }
+    LayoutNode* last_child() { return m_last_child; }
+    const LayoutNode* next_sibling() const { return m_next_sibling; }
+    const LayoutNode* previous_sibling() const { return m_previous_sibling; }
+    const LayoutNode* first_child() const { return m_first_child; }
+    const LayoutNode* last_child() const { return m_last_child; }
+
+    void append_child(Retained<LayoutNode>);
+
+    void set_next_sibling(LayoutNode* node) { m_next_sibling = node; }
+    void set_previous_sibling(LayoutNode* node) { m_previous_sibling = node; }
+
+    template<typename Callback>
+    inline void for_each_child(Callback callback) const
+    {
+        for (auto* node = first_child(); node; node = node->next_sibling())
+            callback(*node);
+    }
+
+    virtual const char* class_name() const { return "LayoutNode"; }
+    virtual bool is_text() const { return false; }
+
+protected:
+    explicit LayoutNode(const Node*);
+
+private:
+    int m_retain_count { 1 };
+    const Node* m_node { nullptr };
+    LayoutNode* m_parent_node { nullptr };
+    LayoutNode* m_first_child { nullptr };
+    LayoutNode* m_last_child { nullptr };
+    LayoutNode* m_next_sibling { nullptr };
+    LayoutNode* m_previous_sibling { nullptr };
+};
+