Implementing custom element's attributeChanged callback in Dartium

tests/html/custom/attribute_changed_callback_test.dart

Index: tests/html/custom/attribute_changed_callback_test.dart
diff --git a/tests/html/custom/attribute_changed_callback_test.dart b/tests/html/custom/attribute_changed_callback_test.dart
index 3a9271a48e1c9f5318ea6b86dc91a92cfe746cc8..1bcc4530d3829a603dfbc6519b5c89474517a637 100644
--- a/tests/html/custom/attribute_changed_callback_test.dart
+++ b/tests/html/custom/attribute_changed_callback_test.dart
@@ -92,6 +92,8 @@ main() {
 
   group('unsupported_on_polyfill', () {
     test('add, change ID', () {
+      B.invocations = [];
+
       var b = new B();
       b.id = 'x';
       expect(B.invocations, ['created', 'id: null => x']);