Don't pass typeExtension argument to native createElement. It's unneeded and causes a problem in Chrome 28 where document.createElement('nav', undefined) results in undefined.

sorvell · sorvell · commit f485280326e4 · 2013-08-16T13:39:05.000-07:00
Helps address (Polymer/polymer#243)
diff --git a/src/CustomElements.js b/src/CustomElements.js
@@ -310,7 +310,7 @@ if (useNative) {
     if (definition) {
       return new definition.ctor();
     }
-    return domCreateElement(tag, typeExtension);
+    return domCreateElement(tag);
   }
 
   function upgradeElement(inElement) {

Original file line number	Diff line number	Diff line change
`@@ -310,7 +310,7 @@ if (useNative) {`
`310`	`310`	`if (definition) {`
`311`	`311`	`return new definition.ctor();`
`312`	`312`	`}`
`313`		`- return domCreateElement(tag, typeExtension);`
	`313`	`+ return domCreateElement(tag);`
`314`	`314`	`}`
`315`	`315`
`316`	`316`	`function upgradeElement(inElement) {`