Fix polyfill templates

Handle cases when elements register before templates are bootstrapped

Fixes Polymer/vulcanize#209

@@ -33,6 +33,12 @@
           'must not be a type-extension, found', this._template,
           'Move inside simple <template>.'));
       }
+      // bootstrap the template if it has not already been
+      if (this._template && !this._template.content && HTMLTemplateElement.bootstrap) {
+        HTMLTemplateElement.decorate(this._template);
+        // recurse if necessary
+        HTMLTemplateElement.bootstrap(this._template.content);
+      }
     },
 
     _stampTemplate: function() {
@@ -60,4 +66,4 @@
 
   });
 
-</script>
+</script>