Fix node_validator xss tests for IE and Firefox

tools/dom/templates/html/impl/impl_Element.darttemplate

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
 class _ChildrenElementList extends ListBase<Element>
     implements NodeListWrapper {
   // Raw Element.
   final Element _element;
@@ skipping 1435 matching lines @@
          if (element.lastChild &&
              element.lastChild !== childNodes[childNodes.length -1]) {
            return true;
          }
          if (element.children) { // On Safari, children can apparently be null.
            if (!((element.children instanceof HTMLCollection) ||
                (element.children instanceof NodeList))) {
              return true;
            }
          }
+         var length = 0;
+         if (element.children) {
+           length = element.children.length;
+         }
+         for (var i = 0; i < length; i++) {
+           var child = element.children[i];
+           // On IE it seems like we sometimes don't see the clobbered attribute,
+           // perhaps as a result of an over-optimization. Also use another route
+           // to check of attributes, children, or lastChild are clobbered. It may
+           // seem silly to check children as we rely on children to do this iteration,
+           // but it seems possible that the access to children might see the real thing,
+           // allowing us to check for clobbering that may show up in other accesses.
+           if (child["id"] == 'attributes' || child["name"] == 'attributes' ||
+               child["id"] == 'lastChild'  || child["name"] == 'lastChild' ||
+               child["id"] == 'children' || child["name"] == 'children') {
+             return true;
+           }
+         }
          return false;
           })(#)''', element);
   }
 $else
 
   static var _namedNodeMap = js.context["NamedNodeMap"];
   static var _htmlCollection = js.context["HTMLCollection"];
   static var _nodeList = js.context["NodeList"];
 
   static bool _hasCorruptedAttributes(Element element) {
@@ skipping 12 matching lines @@
     if (null != children) { // On Safari, children can apparently be null.
       if (!children.instanceof(_htmlCollection) ||
           children.instanceof(_nodeList)) {
         return true;
       }
     }
     return false;
   }
 $endif
 
-  String get _safeTagName {
+  static String _safeTagName(element) {
     String result = 'element tag unavailable';
     try {
-      if (tagName is String) {
-        result = tagName;
+      if (element.tagName is String) {
+        result = element.tagName;
       }
     } catch (e) {}
     return result;
   }
 
 $if DART2JS
   @DomName('Element.offsetHeight')
   @DocsEditable()
   int get offsetHeight => JS('num', '#.offsetHeight', this).round();
 
@@ skipping 211 matching lines @@
   const ScrollAlignment._internal(this._value);
   toString() => 'ScrollAlignment.$_value';
 
   /// Attempt to align the element to the top of the scrollable area.
   static const TOP = const ScrollAlignment._internal('TOP');
   /// Attempt to center the element in the scrollable area.
   static const CENTER = const ScrollAlignment._internal('CENTER');
   /// Attempt to align the element to the bottom of the scrollable area.
   static const BOTTOM = const ScrollAlignment._internal('BOTTOM');
 }