Even more PassRef<RenderStyle>!
<https://webkit.org/b/123147>

Convert more of the WebCore code to use PassRef for RenderStyle
in places where they are known to be non-null.

Re-landing this without region styling since that caused some
assertions last time.

Reviewed by Antti Koivisto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@157854 268f45cc-cd09-0410-ab3c-d52691b4dbfc
StringImpl::lower() should return a PassRef.
<https://webkit.org/b/123190>

Test the waters and hack enough of StringImpl to be able to return
a PassRef<StringImpl> from lower().

Also gave String a constructor that takes a PassRef<StringImpl>.

Reviewed by Antti Koivisto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@157855 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Tighten animation-driven restyle to operate on Element only.
<https://webkit.org/b/122820>

Text nodes are never directly animated, so we can tighten this code
to work on Element only. This happens naturally since the code was
already working with RenderElement everywhere.

Reviewed by Antti Koivisto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@157856 268f45cc-cd09-0410-ab3c-d52691b4dbfc