From 8d7def7208a7e94171c6c5c4a8101b8bda9dd7e1 Mon Sep 17 00:00:00 2001
From: Steven Orvell <sorvell@google.com>
Date: Wed, 10 Apr 2019 16:27:33 -0700
Subject: [PATCH] don't depend on `attachDom` existing.

---
 lib/mixins/element-mixin.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/mixins/element-mixin.js b/lib/mixins/element-mixin.js
index e2e6eebc5e..7690978cea 100644
--- a/lib/mixins/element-mixin.js
+++ b/lib/mixins/element-mixin.js
@@ -672,7 +672,7 @@ export const ElementMixin = dedupingMixin(base => {
       if (n.attachShadow) {
         if (dom) {
           if (!n.shadowRoot) {
-            if (window.ShadyDOM) {
+            if (window.ShadyDOM && ShadyDOM['attachDom']) {
               ShadyDOM['attachDom'](dom, this, {mode: 'open'});
             } else {
               n.attachShadow({mode: 'open'});