<https://webkit.org/b/119963> Use TextNodeTraversal for getting sheet text in StyleElement

Reviewed by Andreas Kling.
        
As a follow-up, mark as crashing a test that is now expected to crash in controlled manner (CRASH()).

Note that the test only ever passed because the amount of data was huge enough (>4GB) for it to take
the special do-nothing code path. With slightly less data the test would hit CRASH() in fastRealloc() like
it does now.

* TestExpectations:
        
    Mark fast/css/giant-stylesheet-crash.html as crashing.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154246 268f45cc-cd09-0410-ab3c-d52691b4dbfc