Use asserts in origin trials layout tests

third_party/WebKit/LayoutTests/http/tests/origin_trials/webexposed/rootscroller-origin-trial-interfaces-script-added.html

Index: third_party/WebKit/LayoutTests/http/tests/origin_trials/webexposed/rootscroller-origin-trial-interfaces-script-added.html
diff --git a/third_party/WebKit/LayoutTests/http/tests/origin_trials/webexposed/rootscroller-origin-trial-interfaces-script-added.html b/third_party/WebKit/LayoutTests/http/tests/origin_trials/webexposed/rootscroller-origin-trial-interfaces-script-added.html
index 138fc11e75274c1489702b717b45996154fa2b1d..07128af57003d91f90514b9b0eab91ec3eeec001 100644
--- a/third_party/WebKit/LayoutTests/http/tests/origin_trials/webexposed/rootscroller-origin-trial-interfaces-script-added.html
+++ b/third_party/WebKit/LayoutTests/http/tests/origin_trials/webexposed/rootscroller-origin-trial-interfaces-script-added.html
@@ -9,19 +9,15 @@
 // generate_token.py  http://127.0.0.1:8000 RootScroller --expire-timestamp=2000000000
 var token = "AuKypT9HyT7fv0cU54WMd1bUmdBYTFED3hKRFWfvxauV8saEM1CoOFLXDd3ApWwJCvimlrGVcqj+0Z9rJL8uFgIAAABUeyJvcmlnaW4iOiAiaHR0cDovLzEyNy4wLjAuMTo4MDAwIiwgImZlYXR1cmUiOiAiUm9vdFNjcm9sbGVyIiwgImV4cGlyeSI6IDIwMDAwMDAwMDB9";
 
+let properties_to_check = {'Document': ['rootScroller']};
+
 test(t => {
-  var interfaces =
-      OriginTrialsHelper.get_interface_names(this, ['Document'],
-                                             {'Document':'rootScroller'});
-  console.log('Interfaces before adding trial token\n' + interfaces);
-}, "RootScroller related interfaces before adding trial token via script.");
+  OriginTrialsHelper.check_properties_missing(this, properties_to_check);
+}, "RootScroller related properties on interfaces before adding trial token via script.");
 
 OriginTrialsHelper.add_token(token);
 
 test(t => {
-  var interfaces =
-      OriginTrialsHelper.get_interface_names(this, ['Document'],
-                                             {'Document':'rootScroller'});
-  console.log('Interfaces after adding trial token\n' + interfaces);
-}, "RootScroller related interfaces after adding trial token via script.");
+  OriginTrialsHelper.check_properties(this, properties_to_check);
+}, "RootScroller related properties on interfaces after adding trial token via script.");
 </script>