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 180 matching lines @@
       isAttr = attrs['is'];
       corrupted = Element._hasCorruptedAttributes(element);
     } catch(e) {}
      var elementText = 'element unprintable';
     try {
       elementText = element.toString();
     } catch(e) {}
     var elementTagName = 'element tag unavailable';
     try {
       elementTagName = element.tagName;
+      if (elementTagName != elementTagName.toString() {

[sra1, 2015/05/27 00:45:18]

1. Parse error - missing ')'.
2. A malicious toString could return 'this'.
3. With --trust-type-annotations or type inference, this could plausibly be
optimized to a null check or `false`.

If you are really checking for a String, use
   if (confuse(elementTagName) is !String) {
     corrupted = true;
   }

[Alan Knight, 2015/05/27 19:54:47]

OK, this doesn't seem worthwhile, took it out.

+        corrupted = true; // The tag name is not a string
+      }
     } catch(e) {}
     _sanitizeElement(element, parent, corrupted, elementText, elementTagName,
         attrs, isAttr);
   }
 
   /// Having done basic sanity checking on the element, and computed the
   /// important attributes we want to check, remove it if it's not valid
   /// or not allowed, either as a whole or particular attributes.
   void _sanitizeElement(Element element, Node parent, bool corrupted,
       String text, String tag, Map attrs, String isAttr) {
@@ skipping 35 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);
     }
   }
 }