Merged r16129 into trunk branch.

Replace MathFloor/Round by HChange if the input representation does not match the output representation

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/22890002

git-svn-id: https://v8.googlecode.com/svn/trunk@16159 ce2b1a6d-e550-0410-aec6-3dcde31c8c00