Revert of Remove the allowfullscreen exemption for the video-specific fullscreen API

LayoutTests/fullscreen/full-screen-iframe-legacy.html

-<p>HTMLVideoElement.webkitEnterFullScreen() in an iframe requires the allowfullscreen attribute</p>
+<p>Test for <a href="https://bugs.webkit.org/show_bug.cgi?id=61461">bug 61461</a>: 
+Handle entering full screen security restrictions</p>
+<p>To test manually, click the video "full screen" button - the page should enter full screen mode.</p>
 <script src="full-screen-test.js"></script>
 <script src="../media/media-file.js"></script>
 <script>
 
 function canplaythrough() {
     var frame = document.getElementById('frame');
 
     runWithKeyDown(function() {
         var video = frame.contentDocument.getElementsByTagName('video')[0];
         video.webkitEnterFullScreen();
     });
 }
 
 function runTest() {
     var frame = document.getElementById('frame');
 
-    waitForEvent(frame.contentDocument, 'webkitfullscreenerror', function() {
+    waitForEvent(frame.contentDocument, 'webkitfullscreenchange', function() {
+            test("document.getElementById('frame').contentDocument.width==document.width")
             endTest();
     });
 
     var video = frame.contentDocument.getElementsByTagName('video')[0];
     var mediaFile = findMediaFile("video", "../../media/content/test");
     video.src = mediaFile;
     video.addEventListener('canplaythrough', canplaythrough);
 }
 </script>
 <iframe id="frame" src="resources/legacy.html" onload="runTest()" width="336" height="256">
 </iframe>