Sync the NodeList interface with the spec

Source/core/dom/NodeList.idl

Index: Source/core/dom/NodeList.idl
diff --git a/Source/core/dom/NodeList.idl b/Source/core/dom/NodeList.idl
index 66cc82045c839b45ca408575ed2d494c3dfd7355..5e549ca9eda012fa93a8b10c969edb7997428163 100644
--- a/Source/core/dom/NodeList.idl
+++ b/Source/core/dom/NodeList.idl
@@ -18,11 +18,14 @@
  * Boston, MA 02110-1301, USA.
  */
 
+// https://dom.spec.whatwg.org/#interface-nodelist
+
 [
     DependentLifetime,
     SetWrapperReferenceFrom=virtualOwnerNode,
     WillBeGarbageCollected,
 ] interface NodeList {
-    getter Node item(unsigned long index);
+    getter Node? item(unsigned long index);
     readonly attribute unsigned long length;
+    // FIXME: iterable<Node>;
 };