Test for bug 90327: webkitCancelFullScreen for iframes

To test manually, click the "Go full screen" button - the page should enter full screen mode and immediately exit again, without crashing.

EVENT(webkitfullscreenchange)
TEST(document.getElementById('frame').contentDocument.webkitIsFullScreen==true) OK
EVENT(webkitfullscreenchange)
TEST(document.getElementById('frame').contentDocument.webkitIsFullScreen==false) OK
END OF TEST