Remove Platform.upgrateCustomElements.

tests/html/utils.dart

 library TestUtils;
 
 import 'dart:async';
 import 'dart:html';
+import 'dart:js' as js;
 import 'dart:typed_data';
 import 'package:unittest/unittest.dart';
 
 /**
  * Verifies that [actual] has the same graph structure as [expected].
  * Detects cycles and DAG structure in Maps and Lists.
  */
 verifyGraph(expected, actual) {
   var eItems = [];
   var aItems = [];
@@ skipping 151 matching lines @@
         ..src = '/packages/custom_element/custom-elements.debug.js';
     document.head.append(script);
     return document.body.on['WebComponentsReady'].first;
   }
   return new Future.value();
 }
 
 Future loadPolyfills() {
   return loadCustomElementPolyfill();
 }
+
+// Pump custom events polyfill events.
+void customElementsTakeRecords() {
+  if (js.context.hasProperty('CustomElements')) {
+    js.context['CustomElements'].callMethod('takeRecords');
+  }
+}