[Refactoring] StyleResolver::matchScopedAuthorRules() could be simpler.

Reviewed by Dimitri Glazkov.

matchScopedAuthorRules() did have some optimization which only
makes sense for heavily nested shadow tree. However, we don't see
such type of usage of Shadow DOM and this looks premature
optimization. This change unified its triple for loop into one,
which makes the code much simpler.

No new tests. Covered by existing tests.

* css/StyleResolver.cpp:
(WebCore::StyleResolver::matchScopedAuthorRules):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@130249 268f45cc-cd09-0410-ab3c-d52691b4dbfc