fix parsing of semantic template interation w/ shadowdom polyfill

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index f8405a0266fa3b24b727761256deef5c5e12ba96..94f7cc301120ac8f04e915d00a9d52b0ef6c5f41 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -21693,6 +21693,7 @@ class TemplateElement extends _HTMLElement native "HTMLTemplateElement" {
     _injectStylesheet();
 
     var templateElement = template;
+    templateElement._templateIsDecorated = true;
     var isNative = templateElement is TemplateElement;
     var bootstrapContents = isNative;
     var liftContents = !isNative;
@@ -21705,12 +21706,11 @@ class TemplateElement extends _HTMLElement native "HTMLTemplateElement" {
             '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();