implement NodeList and consolidate common scope and context retrieval

src/components/script/dom/bindings/codegen/Bindings.conf

@@ -300,14 +300,15 @@ DOMInterfaces = {
         'nodeValue',
         'removeChild',
         'textContent',
+        'childNodes'
     ]
 },
 
 'NodeList': [
 {
-    'nativeType': 'nsINodeList',
-    'prefable': True,
-    'resultNotAddRefed': [ 'item' ]
+    'nativeType': 'NodeList',
+    'pointerType': '@mut ',
+    'resultNotAddRefed': ['item']
 }],
 
 'PaintRequestList': [

src/components/script/dom/bindings/codegen/Node.webidl

@@ -42,8 +42,8 @@ interface Node /*: EventTarget*/ {
   [Pure]
   readonly attribute Element? parentElement;
   boolean hasChildNodes();
-  /*[Constant]
-    readonly attribute NodeList childNodes;*/
+  [Constant]
+  readonly attribute NodeList childNodes;
   [Pure]
   readonly attribute Node? firstChild;
   [Pure]

src/components/script/dom/bindings/codegen/NodeList.webidl

@@ -0,0 +1,16 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * The origin of this IDL file is
+ * http://www.w3.org/TR/2012/WD-dom-20120105/
+ *
+ * Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C
+ * liability, trademark and document use rules apply.
+ */
+
+interface NodeList {
+  readonly attribute unsigned long length;
+  getter Node? item(unsigned long index);
+};