Move paint() to RenderElement
https://bugs.webkit.org/show_bug.cgi?id=122371

Reviewed by Darin Adler.

RenderText does not paint itself (text is painted by line boxes). We can move paint() down
to RenderElement.
        
This also requires some type tightening elsewhere in the code.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@156952 268f45cc-cd09-0410-ab3c-d52691b4dbfc