<style>
    object {
        width: 100px;
        height: 100px;  
    }
</style>
<body>
    <object data="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAADElEQVQIHWNg+M8AAAICAQDpLOrTAAAAAElFTkSuQmCC" type="image/png" />
    <script>
        function toggleVisiblity(element, after) {
            return new Promise((resolve) => {
                setTimeout(() => {
                    if (element.style.display === "none")
                        element.style.display = "block";
                    else
                        element.style.display = "none";
                    resolve();
                }, after);
            });
        }

        if (window.testRunner)
            testRunner.waitUntilDone();

        var element = document.querySelector("object");
        toggleVisiblity(element, 50).then(() => {
            return toggleVisiblity(element, 50);
        }).then(() => {
            if (window.testRunner)
                testRunner.notifyDone();
        });
    </script>
</body>