MIPS: Avoid redundant smi check for Math.abs
MIPS: Avoid redundant smi check for Math.abs

Port r16021 (d79f4450)

BUG=

Review URL: https://codereview.chromium.org/21903003

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@16035 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh