Make CompositingReasonFinder::requiresCompositingForAnimation take RenderStyle*

This makes CompositingReasonFinder::requiresCompositingForAnimation
take a RenderStyle* rather than a RenderObject*.

Review URL: https://codereview.chromium.org/317013005

git-svn-id: svn://svn.chromium.org/blink/trunk@175692 bbb929c8-8fbe-4397-9dbb-9b2b20218538