https://bugs.webkit.org/show_bug.cgi?id=119072

Reviewed by Beth Dakin.

MediaControlTextTrackContainerElement::createTextTrackRepresentationImage() is called
to paint captions into a layer used for fullscreen video. It did the painting using
a subtree paint, but starting at the root RenderView's layer. This is problematic,
because the caption painting is subject to clipping for columns, and any enclosing
overflow:hidden container.

Fix this by starting the paint at the MediaControlTextTrackContainerElement's
renderer's layer. By doing this we don't have to worry about an offset, so no
translation is required.

Also make sure we update layer before grabbing the renderer (in case layout
destroys it).

* html/shadow/MediaControlElements.cpp:
(WebCore::MediaControlTextTrackContainerElement::createTextTrackRepresentationImage):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153112 268f45cc-cd09-0410-ab3c-d52691b4dbfc