Add regression test for optimized version of Math.abs.
Add regression test for optimized version of Math.abs.

This issue was already fixed on bleeding edge, but adding regression
test to get coverage and to make sure it works on the branches.
Review URL: http://codereview.chromium.org/7237022

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@8402 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

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