Refine binding warning so it doesn't incorrectly warn when element is stamped from a template without binding.

Author: sorvell

src/instance/base.js

@@ -24,7 +24,7 @@
     ready: function() {
     },
     createdCallback: function() {
-      if (this.templateInstance) {
+      if (this.templateInstance && this.templateInstance.model) {
         console.warn('Attributes on ' + this.localName + ' were data bound ' +
             'prior to Polymer upgrading the element. This may result in ' +
             'incorrect binding types.');