Move id attribute to parent Element interface

Source/core/dom/Element.idl

Index: Source/core/dom/Element.idl
diff --git a/Source/core/dom/Element.idl b/Source/core/dom/Element.idl
index 29954ca546a97de5f0fbf4cd661dbaef9c8fdcdd..cc9631f404b681a8a3d3372586c3df7c73d64032 100644
--- a/Source/core/dom/Element.idl
+++ b/Source/core/dom/Element.idl
@@ -59,6 +59,11 @@
 
     [PerWorldBindings] readonly attribute CSSStyleDeclaration style;
 
+    // DOM4
+    // iht.com relies on id returning the empty string when no id is present.
+    // Other browsers do this as well. So we don't convert null to JS null.
+    [Reflect] attribute DOMString id;
+
     // Common extensions
 
     [PerWorldBindings] readonly attribute long offsetLeft;