Split NonDocumentTypeChildNode from ChildNode

Source/core/dom/NonDocumentTypeChildNode.idl

Index: Source/core/dom/NonDocumentTypeChildNode.idl
diff --git a/Source/core/dom/NonDocumentTypeChildNode.idl b/Source/core/dom/NonDocumentTypeChildNode.idl
new file mode 100644
index 0000000000000000000000000000000000000000..b2883c41321802b34476e50ab63670f90fa6ad7a
--- /dev/null
+++ b/Source/core/dom/NonDocumentTypeChildNode.idl
@@ -0,0 +1,13 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// https://dom.spec.whatwg.org/#interface-nondocumenttypechildnode
+
+[
+    LegacyTreatAsPartialInterface,
+    NoInterfaceObject, // Always used on target of 'implements'
+] interface NonDocumentTypeChildNode {
+    [PerWorldBindings] readonly attribute Element previousElementSibling;
+    [PerWorldBindings] readonly attribute Element nextElementSibling;
+};