De-flaking custom element test.

tests/html/custom_elements_test.dart

Index: tests/html/custom_elements_test.dart
diff --git a/tests/html/custom_elements_test.dart b/tests/html/custom_elements_test.dart
index 43c1bf32fa71c31c3d2fd6ad494ccfdd922adfde..8f627e781a7d626c39515ffcc6519d290d890047 100644
--- a/tests/html/custom_elements_test.dart
+++ b/tests/html/custom_elements_test.dart
@@ -38,8 +38,11 @@ class NotAnElement {}
 
 loadPolyfills() {
   if (!document.supportsRegister) {
+    // Cache blocker is a workaround for:
+    // https://code.google.com/p/dart/issues/detail?id=11834
+    var cacheBlocker = new DateTime.now().millisecondsSinceEpoch;
     return HttpRequest.getString('/root_dart/pkg/custom_element/lib/'
-      'custom-elements.debug.js').then((code) {
+      'custom-elements.debug.js?cacheBlock=$cacheBlocker').then((code) {
       document.head.children.add(new ScriptElement()..text = code);
     });
   }