Make sanitizer tests handle IE11, where tagName can't be clobbered

tools/dom/src/Validators.dart

 // Copyright (c) 2013, 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 dart.dom.html;
 
 
 /**
  * Interface used to validate that only accepted elements and attributes are
  * allowed while parsing HTML strings into DOM nodes.
@@ skipping 235 matching lines @@
     if (element is TemplateElement) {
       TemplateElement template = element;
       sanitizeTree(template.content);
      }
   }
 
   /// Sanitize the node and its children recursively.
   void sanitizeNode(Node node, Node parent) {
     switch (node.nodeType) {
       case Node.ELEMENT_NODE:
-        _sanitizeUntrustedElement(node, parent); 
+        _sanitizeUntrustedElement(node, parent);
         break;
       case Node.COMMENT_NODE:
       case Node.DOCUMENT_FRAGMENT_NODE:
       case Node.TEXT_NODE:
       case Node.CDATA_SECTION_NODE:
         break;
       default:
         _removeNode(node, parent);
     }
   }
 }