cherry pick https://github.com/Polymer/ShadowDOM/pull/506

pkg/web_components/lib/platform.concat.js

 /**
  * Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
  * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
  * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
  * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
  * Code distributed by Google as part of the polymer project is also
  * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
  */
 
 window.Platform = window.Platform || {};
@@ skipping 2001 matching lines @@
     try {
       return Object.getOwnPropertyDescriptor(source, name);
     } catch (ex) {
       // JSC and V8 both use data properties instead of accessors which can
       // cause getting the property desciptor to throw an exception.
       // https://bugs.webkit.org/show_bug.cgi?id=49739
       return dummyDescriptor;
     }
   }
 
+  // Safari 8 exposes WebIDL attributes as an invalid accessor property. Its
+  // descriptor has {get: undefined, set: undefined}. We therefore ignore the
+  // shape of the descriptor and make all properties read-write.
+  // https://bugs.webkit.org/show_bug.cgi?id=49739
+  var isBrokenSafari = function() {
+    var descr = Object.getOwnPropertyDescriptor(Node.prototype, 'nodeType');
+    return !!descr && 'set' in descr;
+  }();
+
   function installProperty(source, target, allowMethod, opt_blacklist) {
     var names = getOwnPropertyNames(source);
     for (var i = 0; i < names.length; i++) {
       var name = names[i];
       if (name === 'polymerBlackList_')
         continue;
 
       if (name in target)
         continue;
 
@@ skipping 10 matching lines @@
         target[name] = getMethod(name);
         continue;
       }
 
       var isEvent = isEventHandlerName(name);
       if (isEvent)
         getter = scope.getEventHandlerGetter(name);
       else
         getter = getGetter(name);
 
-      if (descriptor.writable || descriptor.set) {
+      if (descriptor.writable || descriptor.set || isBrokenSafari) {
         if (isEvent)
           setter = scope.getEventHandlerSetter(name);
         else
           setter = getSetter(name);
       }
 
       defineProperty(target, name, {
         get: getter,
         set: setter,
         configurable: descriptor.configurable,
@@ skipping 10194 matching lines @@
   // exports
 
   scope.marshal = marshal;
   // `module` confuses commonjs detectors
   scope.modularize = module;
   scope.using = using;
 
 })(window);
 
 //# sourceMappingURL=platform.concat.js.map