From a6694b7f7a6d06149fbcb06d63af99a9e56c6375 Mon Sep 17 00:00:00 2001
From: Steven Orvell <sorvell@google.com>
Date: Thu, 3 Sep 2015 12:56:27 -0700
Subject: [PATCH] Fixes #2403

---
 src/lib/polymer-bootstrap.html | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/lib/polymer-bootstrap.html b/src/lib/polymer-bootstrap.html
index 3386d515bf..cdfc63a4a7 100644
--- a/src/lib/polymer-bootstrap.html
+++ b/src/lib/polymer-bootstrap.html
@@ -35,9 +35,13 @@
       // this may have resulted in a new prototype being created
       prototype = factory.prototype;
       var options = {
-        prototype: prototype,
-        extends: prototype.extends
+        prototype: prototype
       };
+      // NOTE: we're specifically supporting older Chrome versions here 
+      // (specifically Chrome 39) that throw when options.extends is undefined.
+      if (prototype.extends) {
+        options.extends = prototype.extends;
+      }
       Polymer.telemetry._registrate(prototype);
       document.registerElement(prototype.is, options);
       return factory;