bindings: Fixes push_messaging/interfaces.html test.

LayoutTests/http/tests/push_messaging/resources/interfaces-worker.js

Index: LayoutTests/http/tests/push_messaging/resources/interfaces-worker.js
diff --git a/LayoutTests/http/tests/push_messaging/resources/interfaces-worker.js b/LayoutTests/http/tests/push_messaging/resources/interfaces-worker.js
index 5f54d540c5468f93e5ec5d752bcf9f9e8f5e9c31..f9832695acb0938ff79457454e444587bbf7abea 100644
--- a/LayoutTests/http/tests/push_messaging/resources/interfaces-worker.js
+++ b/LayoutTests/http/tests/push_messaging/resources/interfaces-worker.js
@@ -15,7 +15,7 @@ test(function() {
 
 test(function() {
     assert_own_property(self, 'PushManager', 'PushManager needs to be exposed as a global.');
-    assert_own_property(registration, 'pushManager', 'PushManager needs to be exposed on the registration.');
+    assert_will_be_idl_attribute(registration, 'pushManager', 'PushManager needs to be exposed on the registration.');
 
     assert_inherits(registration.pushManager, 'subscribe');
     assert_inherits(registration.pushManager, 'getSubscription');