Convert PerformanceEntry.navigationId to a coarse counter

Change-Id: I292ce8ea5df71515ae3fcfffcd06e559148c9964
diff --git a/performance-timeline/navigation-id-worker-created-entries.html b/performance-timeline/navigation-id-worker-created-entries.html
index 96fc57b..899d51e 100644
--- a/performance-timeline/navigation-id-worker-created-entries.html
+++ b/performance-timeline/navigation-id-worker-created-entries.html
@@ -18,10 +18,10 @@
         worker.postMessage('');
       });
 
-      assert_equals(navigationId.length, 0,
+      assert_equals(navigationId, 0,
         'Navigation id of performance entries created by a worker should be empty.');
     }, 'Navigation id of performance entries created by workers should be empty');
   </script>
 </body>
 
-</html>
\ No newline at end of file
+</html>