Fix node validation for SVG foreignobject tag

tools/dom/src/NodeValidatorBuilder.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;
 
 
 /**
  * Class which helps construct standard node validation policies.
  *
@@ skipping 437 matching lines @@
 }
 
 
 class _SvgNodeValidator implements NodeValidator {
   bool allowsElement(Element element) {
     if (element is svg.ScriptElement) {
       return false;
     }
     // Firefox 37 has issues with creating foreign elements inside a
     // foreignobject tag as SvgElement. We don't want foreignobject contents
-    // anyway, so just remove the whole tree outright.
-    if (element is svg.ForeignObjectElement) {
+    // anyway, so just remove the whole tree outright. And we can't rely
+    // on IE recognizing the SvgForeignObject type, so go by tagName. Bug 23144
+    if (element is svg.SvgElement && element.tagName == 'foreignObject') {
       return false;
     }
     if (element is svg.SvgElement) {
       return true;
     }
     return false;
   }
 
   bool allowsAttribute(Element element, String attributeName, String value) {
     if (attributeName == 'is' || attributeName.startsWith('on')) {
       return false;
     }
     return allowsElement(element);
   }
 }