Use CascadedProperties for page and keyframe style resolution as well.

Use CascadedProperties for page and keyframe style resolution as well.
<https://webkit.org/b/125997>

Port StyleResolver's styleForKeyframe() and styleForPage() over to
the new property cascading code. Neither of them care about !important
or matched properties caches, so the code is very simple.

Removed the old applyMatchedProperties and applyProperties code with
low/high priority passes.

Reviewed by Antti Koivisto.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@160852 268f45cc-cd09-0410-ab3c-d52691b4dbfc