Sync HTML element interfaces C-D with the spec

Source/core/html/HTMLDialogElement.idl

Index: Source/core/html/HTMLDialogElement.idl
diff --git a/Source/core/html/HTMLDialogElement.idl b/Source/core/html/HTMLDialogElement.idl
index 702653db8ce1dbdb07eec48f5a6f4e69c17cce2e..75d5d14ad285537ca24104f01f237eb5a59159cd 100644
--- a/Source/core/html/HTMLDialogElement.idl
+++ b/Source/core/html/HTMLDialogElement.idl
@@ -23,11 +23,14 @@
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+// https://html.spec.whatwg.org/#htmldialogelement
+
 interface HTMLDialogElement : HTMLElement {
     [Reflect] attribute boolean open;
     attribute DOMString returnValue;
-    [RaisesException] void close(optional DOMString returnValue = null);
+    // FIXME: show() and showModal() should take an anchor argument.
     void show();
     [RaisesException] void showModal();
+    // FIXME: The returnValue argument should have no default value.
+    [RaisesException] void close(optional DOMString returnValue = null);
 };
-