<rdar://problem/9515650> 30 second rewind button obscured in fullscreen controller...

<rdar://problem/9515650> 30 second rewind button obscured in fullscreen controller when video uses custom inline controls
https://bugs.webkit.org/show_bug.cgi?id=61714

Reviewed by Darin Adler.

* dom/Document.cpp:
(WebCore::Document::webkitDidEnterFullScreenForElement): Call didBecomeFullscreenElement() on the
new full screen element.
(WebCore::Document::webkitWillExitFullScreenForElement): Call willStopBeingFullscreenElement() on
the full screen element.
* dom/Element.h:
(WebCore::Element::didBecomeFullscreenElement): Added with a default implementation that does nothing.
(WebCore::Element::willStopBeingFullscreenElement): Ditto.
* html/HTMLMediaElement.cpp:
(WebCore::HTMLMediaElement::didBecomeFullscreenElement): Added this override, which calls
MediaControls::enteredFullscreen().
(WebCore::HTMLMediaElement::willStopBeingFullscreenElement): Added this override, which calls
MediaControls::exitedFullscreen().
* html/HTMLMediaElement.h:
* html/shadow/MediaControlElements.cpp:
(WebCore::MediaControlFullscreenButtonElement::preDispatchEventHandler): Removed calls to
enteredFullscreen() and exitedFullscreen() from here, since they are now called in response to
changes to the fullscreen-ness of the element.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@87657 268f45cc-cd09-0410-ab3c-d52691b4dbfc