Merged r18737 into trunk branch.

Fixed floor-of-div optimization.

BUG=334708
LOG=N
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/144023008

git-svn-id: https://v8.googlecode.com/svn/trunk@18747 ce2b1a6d-e550-0410-aec6-3dcde31c8c00