LibWeb: Set inertness of HTMLElement when inert attribute is changed

Author: https://github.com/tcl3
Commit: a9ffc6359a
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3475
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/DOM/Node.cpp

@@ -2110,6 +2110,17 @@ bool Node::is_default_namespace(Optional<String> namespace_) const
     return default_namespace == namespace_;
 }
 
+bool Node::is_inert() const
+{
+    if (auto* html_element = as_if<HTML::HTMLElement>(*this))
+        return html_element->is_inert();
+
+    if (auto* enclosing_html_element = this->enclosing_html_element())
+        return enclosing_html_element->is_inert();
+
+    return false;
+}
+
 // https://dom.spec.whatwg.org/#in-a-document-tree
 bool Node::in_a_document_tree() const
 {