R=bmeurer@chromium.org
TEST=compiler-unittests/JSBuiltinReducerTest.MathFround

Review URL: https://codereview.chromium.org/594183004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24187 ce2b1a6d-e550-0410-aec6-3dcde31c8c00