LibWeb: Strip out the mutation event logic from TreeNode

This will instead be done by Node, as they need to occur at precise
steps of the mutation algorithms. Additionally, some of the events
may need to be run multiple times. For example, the removal steps
is run for all the shadow-including descendants of the node that
just got removed.

Userland/Libraries/LibWeb/TreeNode.h

@@ -99,10 +99,10 @@ public:
 
     bool is_ancestor_of(const TreeNode&) const;
 
+    void append_child(NonnullRefPtr<T> node);
     void prepend_child(NonnullRefPtr<T> node);
-    void append_child(NonnullRefPtr<T> node, bool notify = true);
-    void insert_before(NonnullRefPtr<T> node, RefPtr<T> child, bool notify = true);
-    NonnullRefPtr<T> remove_child(NonnullRefPtr<T> node);
+    void insert_before(NonnullRefPtr<T> node, RefPtr<T> child);
+    void remove_child(NonnullRefPtr<T> node);
 
     void remove_all_children();
 
@@ -332,8 +332,9 @@ inline void TreeNode<T>::remove_all_children()
         remove_child(child.release_nonnull());
 }
 
+
 template<typename T>
-inline NonnullRefPtr<T> TreeNode<T>::remove_child(NonnullRefPtr<T> node)
+inline void TreeNode<T>::remove_child(NonnullRefPtr<T> node)
 {
     VERIFY(node->m_parent == this);
 
@@ -353,17 +354,11 @@ inline NonnullRefPtr<T> TreeNode<T>::remove_child(NonnullRefPtr<T> node)
     node->m_previous_sibling = nullptr;
     node->m_parent = nullptr;
 
-    node->removed_from(static_cast<T&>(*this));
-
     node->unref();
-
-    static_cast<T*>(this)->children_changed();
-
-    return node;
 }
 
 template<typename T>
-inline void TreeNode<T>::append_child(NonnullRefPtr<T> node, bool notify)
+inline void TreeNode<T>::append_child(NonnullRefPtr<T> node)
 {
     VERIFY(!node->m_parent);
 
@@ -377,26 +372,18 @@ inline void TreeNode<T>::append_child(NonnullRefPtr<T> node, bool notify)
     m_last_child = node.ptr();
     if (!m_first_child)
         m_first_child = m_last_child;
-    if (notify)
-        node->inserted_into(static_cast<T&>(*this));
     [[maybe_unused]] auto& rc = node.leak_ref();
-
-    if (notify)
-        static_cast<T*>(this)->children_changed();
 }
 
 template<typename T>
-inline void TreeNode<T>::insert_before(NonnullRefPtr<T> node, RefPtr<T> child, bool notify)
+inline void TreeNode<T>::insert_before(NonnullRefPtr<T> node, RefPtr<T> child)
 {
     if (!child)
-        return append_child(move(node), notify);
+        return append_child(move(node));
 
     VERIFY(!node->m_parent);
     VERIFY(child->parent() == this);
 
-    if (!static_cast<T*>(this)->is_child_allowed(*node))
-        return;
-
     node->m_previous_sibling = child->m_previous_sibling;
     node->m_next_sibling = child;
 
@@ -409,12 +396,7 @@ inline void TreeNode<T>::insert_before(NonnullRefPtr<T> node, RefPtr<T> child, b
     child->m_previous_sibling = node;
 
     node->m_parent = static_cast<T*>(this);
-    if (notify)
-        node->inserted_into(static_cast<T&>(*this));
     [[maybe_unused]] auto& rc = node.leak_ref();
-
-    if (notify)
-        static_cast<T*>(this)->children_changed();
 }
 
 template<typename T>