RenderElement::rendererForRootBackground() should return a reference.
<https://webkit.org/b/125735>

This function always finds a renderer to return.

Reviewed by Antti Koivisto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160595 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Move a couple of inlines from RenderObject to RenderElement.
<https://webkit.org/b/125734>

Take most of the inline functions on RenderObject that call style()
and move them over to RenderElement where style() is branchless.

Reviewed by Antti Koivisto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160596 268f45cc-cd09-0410-ab3c-d52691b4dbfc