Layout Tests: Remove assert_will_be_idl_attribute() helper

third_party/WebKit/LayoutTests/http/tests/background_sync/resources/interfaces-worker.js

Index: third_party/WebKit/LayoutTests/http/tests/background_sync/resources/interfaces-worker.js
diff --git a/third_party/WebKit/LayoutTests/http/tests/background_sync/resources/interfaces-worker.js b/third_party/WebKit/LayoutTests/http/tests/background_sync/resources/interfaces-worker.js
index 0df2dca6c08dad07d016d8d5805de99656c531fe..679cf3d03ad30c123e048683b0298d9ca0e43c7e 100644
--- a/third_party/WebKit/LayoutTests/http/tests/background_sync/resources/interfaces-worker.js
+++ b/third_party/WebKit/LayoutTests/http/tests/background_sync/resources/interfaces-worker.js
@@ -1,5 +1,4 @@
 importScripts('/resources/testharness.js');
-importScripts('/resources/testharness-helpers.js');
 
 test(function() {
     assert_own_property(self, 'SyncManager', 'SyncManager needs to be exposed as a global.');
@@ -13,10 +12,11 @@ test(function() {
 test(function() {
     assert_own_property(self, 'SyncEvent');
 
-    assert_will_be_idl_attribute(SyncEvent.prototype, 'tag');
+    var instance = new SyncEvent('dummy', {tag: ''});
+    assert_idl_attribute(instance, 'tag');
+    assert_idl_attribute(instance, 'lastChance');
 
     // SyncEvent should be extending ExtendableEvent.
     assert_inherits(SyncEvent.prototype, 'waitUntil');
 
 }, 'SyncEvent should be exposed and have the expected interface.');
-