Restore the HTMLVideoElement-specific prefixed fullscreen API behind a flag

LayoutTests/media/video-prefixed-fullscreen-expected.txt

Index: LayoutTests/media/video-prefixed-fullscreen-expected.txt
diff --git a/LayoutTests/media/video-prefixed-fullscreen-expected.txt b/LayoutTests/media/video-prefixed-fullscreen-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..31040cb15230cdf1ec8ddd508aced1861e367194
--- /dev/null
+++ b/LayoutTests/media/video-prefixed-fullscreen-expected.txt
@@ -0,0 +1,25 @@
+CONSOLE WARNING: 'HTMLVideoElement.webkitSupportsFullscreen' is deprecated. Its value is true if the video is loaded.
+CONSOLE WARNING: 'HTMLVideoElement.webkitDisplayingFullscreen' is deprecated. Please use the 'fullscreenchange' and 'webkitfullscreenchange' events instead.
+CONSOLE WARNING: 'HTMLVideoElement.webkitEnterFullscreen()' is deprecated. Please use 'Element.requestFullscreen()' and 'Element.webkitRequestFullscreen()' instead.
+CONSOLE WARNING: 'HTMLVideoElement.webkitExitFullscreen()' is deprecated. Please use 'Document.exitFullscreen()' and 'Document.webkitExitFullscreen()' instead.
+Test the prefixed HTMLVideoElement fullscreen API
+
+EXPECTED (video.webkitSupportsFullscreen == 'false') OK
+EXPECTED (video.webkitDisplayingFullscreen == 'false') OK
+EVENT(loadeddata)
+EXPECTED (video.webkitSupportsFullscreen == 'true') OK
+EXPECTED (video.webkitDisplayingFullscreen == 'false') OK
+RUN(video.webkitEnterFullscreen())
+EVENT(webkitfullscreenerror)
+EXPECTED (video.webkitSupportsFullscreen == 'true') OK
+EXPECTED (video.webkitDisplayingFullscreen == 'false') OK
+RUN(video.webkitEnterFullscreen())
+EVENT(webkitfullscreenchange)
+EXPECTED (video.webkitSupportsFullscreen == 'true') OK
+EXPECTED (video.webkitDisplayingFullscreen == 'true') OK
+RUN(video.webkitExitFullscreen())
+EVENT(webkitfullscreenchange)
+EXPECTED (video.webkitSupportsFullscreen == 'true') OK
+EXPECTED (video.webkitDisplayingFullscreen == 'false') OK
+END OF TEST
+