LibWeb: Implement the <summary> element

Userland/Libraries/LibWeb/HTML/HTMLSummaryElement.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/ARIA/Roles.h>
+#include <LibWeb/HTML/HTMLElement.h>
+
+namespace Web::HTML {
+
+class HTMLSummaryElement final : public HTMLElement {
+    WEB_PLATFORM_OBJECT(HTMLSummaryElement, HTMLElement);
+
+public:
+    virtual ~HTMLSummaryElement() override;
+
+    // https://www.w3.org/TR/html-aria/#el-details
+    virtual Optional<ARIA::Role> default_role() const override { return ARIA::Role::button; };
+
+    bool is_summary_for_its_parent_details();
+
+private:
+    HTMLSummaryElement(DOM::Document&, DOM::QualifiedName);
+
+    virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
+};
+
+}