fix parsing of semantic template interation w/ shadowdom polyfill

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

 // 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.
 
 // WARNING: Do not edit - generated code.
 
 part of $LIBRARYNAME;
 
 
 /**
@@ skipping 117 matching lines @@
    * already decorated.
    */
   @Experimental()
   static bool decorate(Element template, [Element instanceRef]) {
     // == true check because it starts as a null field.
     if (template._templateIsDecorated == true) return false;
 
     _injectStylesheet();
 
     var templateElement = template;
+    templateElement._templateIsDecorated = true;
     var isNative = templateElement is TemplateElement;
     var bootstrapContents = isNative;
     var liftContents = !isNative;
     var liftRoot = false;
 
     if (!isNative && templateElement._isAttributeTemplate) {
       if (instanceRef != null) {
         // TODO(jmesserly): this is just an assert in MDV.
         throw new ArgumentError('instanceRef should not be supplied for '
             'attribute templates.');
       }
       templateElement = _extractTemplateFromAttributeTemplate(template);
+      templateElement._templateIsDecorated = true;
       isNative = templateElement is TemplateElement;
       liftRoot = true;
      }
 
-    templateElement._templateIsDecorated = true;
-
     if (!isNative) {
       var doc = _getTemplateContentsOwner(templateElement.document);
       templateElement._templateContent = doc.createDocumentFragment();
     }
 
     if (instanceRef != null) {
       // template is contained within an instance, its direct content must be
       // empty
       templateElement._templateInstanceRef = instanceRef;
     } else if (liftContents) {
@@ skipping 126 matching lines @@
     document.head.append(style);
   }
 
   /**
    * A mapping of names to Custom Syntax objects. See [CustomBindingSyntax] for
    * more information.
    */
   @Experimental()
   static Map<String, CustomBindingSyntax> syntax = {};
 }