                       URL.revokeObjectURL(bogusURL);
                    } else {
                        assert_unreached("invalid case");
                    }

                    var video = document.createElement("video");
                    video.preload = preload;
                    document.body.appendChild(video);
                    test.add_cleanup(function() { document.body.removeChild(video); });

                    mediaSource.addEventListener("sourceopen", test.unreached_func("'sourceopen