RenderBlock should not reach inside FloatingObjects and walk it floating object set manually

I also fixed the ordering of an if to avoid the expensive descendantChild check.

BUG=271774
R=bjonesbe@adobe.com, ojan@chromium.org

Review URL: https://codereview.chromium.org/22890004

git-svn-id: svn://svn.chromium.org/blink/trunk@156050 bbb929c8-8fbe-4397-9dbb-9b2b20218538