Integrating fix for IE9 custom elements upgrade

pkg/custom_element/lib/custom-elements.debug.js

 // Copyright (c) 2012 The Polymer Authors. All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //    * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //    * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
@@ skipping 1158 matching lines @@
     // TODO(sjmiles): 'used' allows us to only copy the 'youngest' version of
     // any property. This set should be precalculated. We also need to
     // consider this for supporting 'super'.
     var used = {};
     // start with inSrc
     var p = inSrc;
     // sometimes the default is HTMLUnknownElement.prototype instead of
     // HTMLElement.prototype, so we add a test
     // the idea is to avoid mixing in native prototypes, so adding
     // the second test is WLOG
-    while (p !== inNative && p !== HTMLUnknownElement.prototype) {
+    while (p && p !== inNative && p !== HTMLUnknownElement.prototype) {
       var keys = Object.getOwnPropertyNames(p);
       for (var i=0, k; k=keys[i]; i++) {
         if (!used[k]) {
           Object.defineProperty(inTarget, k,
               Object.getOwnPropertyDescriptor(p, k));
           used[k] = 1;
         }
       }
       p = Object.getPrototypeOf(p);
     }
@@ skipping 270 matching lines @@
 
   // override
   fns.forEach(function(fn) {
     CustomElements[fn] = function(inNode) {
       return original[fn](ShadowDOMPolyfill.wrapIfNeeded(inNode));
     };
   });
 }
 
 })();