Add FeatureObserver for marquee and reflection
https://bugs.webkit.org/show_bug.cgi?id=111118

Reviewed by Simon Fraser.

Refactoring covered by existing tests.

* page/FeatureObserver.h:
* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::styleChanged):
Added some instrumentation for reflection and marquee as they are both prefixed and this would help
to know their popularity on the web. Marquee was split between <marquee> (HTMLMarqueeElement) and
overflow: -webkit-marquee (CSSOverflowMarquee).


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144456 268f45cc-cd09-0410-ab3c-d52691b4dbfc