fix parsing of semantic template interation w/ shadowdom polyfill

sdk/lib/html/dart2js/html_dart2js.dart

 /// The Dart HTML library.
 ///
 /// For examples, see
 /// [Dart HTML5 Samples](https://github.com/dart-lang/dart-html5-samples)
 /// on Github.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide Symbol, deprecated;
@@ skipping 21425 matching lines @@
  *     ...
  *     query('template').bindingDelegate = new MySyntax();
  *     query('template').model = new MyModel();
  *
  * See <https://github.com/polymer-project/mdv/blob/master/docs/syntax.md> for
  * more information about Custom Syntax.
  */
 // TODO(jmesserly): move this type to the MDV package? Two issues: we'd lose
 // type annotation on [Element.bindingDelegate], and "mdv" is normally imported
 // with a prefix.
+@Experimental()
 abstract class BindingDelegate {
   /**
    * This syntax method allows for a custom interpretation of the contents of
    * mustaches (`{{` ... `}}`).
    *
    * When a template is inserting an instance, it will invoke this method for
    * each mustache which is encountered. The function is invoked with four
    * arguments:
    *
    * - [model]: The data context for which this instance is being created.
@@ skipping 92 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 7888 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }