<!DOCTYPE html>
<html>
<head>
    <script>
        function load() {
            window.webkit.messageHandlers.fullscreenStateChangeHandler.postMessage('load');
        }
        document.addEventListener('webkitfullscreenchange', function(event) {
            window.webkit.messageHandlers.fullscreenStateChangeHandler.postMessage('fullscreenchange');
        });
        document.addEventListener('mousedown', function(event) {
            // Toggle fullscreen
            var target = document.getElementById('target');
            if (document.webkitFullscreenElement == target)
                document.webkitExitFullscreen();
            else
                target.webkitRequestFullScreen();
        });
    </script>
    <style>
    #target {
        background-color: red;
        width: 150px;
        height: 150px;
    }
    </style>
</head>
<body onload="load()">
    <div id="target"></div>
</body>
</html>