Implemet :lang() pseudo class support for the WebVTT ::cue pseudo element
https://bugs.webkit.org/show_bug.cgi?id=105478

Patch by Dima Gorbik <dgorbik@apple.com> on 2013-02-04
Reviewed by Antti Koivisto.

Source/WebCore:

In WebVTT lang is preprocessed and stored in the lang attribute of the element,
so we access it instead of walking up the tree the way it is done in HTML.

Existing tests were modified to cover this case.

* css/SelectorChecker.cpp:
(WebCore::SelectorChecker::checkOne):

LayoutTests:

* media/track/captions-webvtt/styling-lang.vtt:
* media/track/track-css-matching-lang-expected.txt:
* media/track/track-css-matching-lang.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141795 268f45cc-cd09-0410-ab3c-d52691b4dbfc