LibWeb: Support the ariaActiveDescendantElement IDL attribute

Author: https://github.com/sideshowbarker
Commit: 1be55fe793
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3085
Reviewed-by: https://github.com/tcl3 ✅

Libraries/LibWeb/DOM/Element.cpp

@@ -96,6 +96,7 @@ void Element::visit_edges(Cell::Visitor& visitor)
     SlottableMixin::visit_edges(visitor);
     Animatable::visit_edges(visitor);
 
+    visitor.visit(m_aria_active_descendant_element);
     visitor.visit(m_attributes);
     visitor.visit(m_inline_style);
     visitor.visit(m_class_list);
@@ -2926,6 +2927,10 @@ void Element::attribute_changed(FlyString const& local_name, Optional<String> co
             m_dir = Dir::Auto;
         else
             m_dir = {};
+    } else if (local_name == ARIA::AttributeNames::aria_active_descendant) {
+        // https://html.spec.whatwg.org/multipage/common-dom-interfaces.html#reflecting-content-attributes-in-idl-attributes:concept-element-attributes-change-ext
+        // Set element's explicitly set attr-element to null.
+        m_aria_active_descendant_element = nullptr;
     }
 }
 

Libraries/LibWeb/DOM/Element.h

@@ -295,6 +295,9 @@ public:
     ENUMERATE_ARIA_ATTRIBUTES
 #undef __ENUMERATE_ARIA_ATTRIBUTE
 
+    GC::Ptr<DOM::Element> aria_active_descendant_element() { return m_aria_active_descendant_element; }
+    void set_aria_active_descendant_element(GC::Ptr<DOM::Element> value) { m_aria_active_descendant_element = value; }
+
     virtual bool exclude_from_accessibility_tree() const override;
 
     virtual bool include_in_accessibility_tree() const override;
@@ -464,6 +467,8 @@ private:
     bool m_in_top_layer { false };
 
     OwnPtr<CSS::CountersSet> m_counters_set;
+
+    GC::Ptr<DOM::Element> m_aria_active_descendant_element;
 };
 
 template<>