HTML: do not test IDL specifics in iframe load event test (#19691)

Author: annevk

html/semantics/embedded-content/the-iframe-element/iframe-load-event.html

@@ -8,17 +8,15 @@
 async_test(function(t) {
   var obj = document.createElement("iframe");
   obj.onload = t.step_func_done(function(e){
-    assert_true(obj.contentWindow instanceof Window, "The iframe element should represent a nested browsing context.")
+    assert_not_equals(obj.contentWindow, null, "The iframe element should represent a nested browsing context.")
     assert_equals(Object.getPrototypeOf(e).constructor, Event, "The load event should use the Event interface.");
     assert_true(e.isTrusted, "The load event should be a trusted event.");
     assert_false(e.cancelable, "The load event should not be a cancelable event.");
     assert_false(e.bubbles, "The load event should not be a bubble event.");
     assert_equals(e.target, obj, "The load event target should be the corresponding object element.");
   });
 
-  obj.onerror = t.step_func_done(function(e){
-    assert_unreached("The error event should not be fired.");
-  });
+  obj.onerror = t.unreached_func("The error event should not be fired.");
 
   var url = URL.createObjectURL(new Blob([""], { type: "text/html" }));
 
@@ -29,20 +27,17 @@
 async_test(function(t) {
   var obj = document.createElement("iframe");
   obj.onload = t.step_func_done(function(e){
-    assert_true(obj.contentWindow instanceof Window, "The object element should represent a nested browsing context.")
+    assert_not_equals(obj.contentWindow, null, "The object element should represent a nested browsing context.")
     assert_equals(Object.getPrototypeOf(e).constructor, Event, "The load event should use the Event interface.");
     assert_true(e.isTrusted, "The load event should be a trusted event.");
     assert_false(e.cancelable, "The load event should not be a cancelable event.");
     assert_false(e.bubbles, "The load event should not be a bubble event.");
     assert_equals(e.target, obj, "The load event target should be the corresponding object element.");
   });
 
-  obj.onerror = t.step_func_done(function(e){
-    assert_unreached("The error event should not be fired.");
-  });
+  obj.onerror = t.unreached_func("The error event should not be fired.");
 
   document.body.appendChild(obj);
 }, "load event of initial about:blank");
-
 </script>
 </body>