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 3ff4de478d50a34b5b81de3802c730fb7732a4fc..ec9e4c41606952cc9122272346187a92d483c126 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -33352,6 +33352,19 @@ class Platform {
    * error.
    */
   static final supportsSimd = false;
+
+  /**
+   * Upgrade all custom elements in the subtree which have not been upgraded.
+   *
+   * This is needed to cover timing scenarios which the custom element polyfill
+   * does not cover.
+   */
+  static void upgradeCustomElements(Node node) {
+    if (JS('bool', '(#.CustomElements && #.CustomElements.upgradeAll)',
+        window, window)) {
+      JS('', '#.CustomElements.upgradeAll(#)', window, node);
+    }
+  }
 }
 // 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