Fix EstimateMarkingStepSizeTest.

R=wingo@igalia.com
TBR=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/494683002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23237 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Implement Math.expm1 using port from fdlibm.

R=rtoy@chromium.org
BUG=v8:3479
LOG=N

Review URL: https://codereview.chromium.org/465353002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23238 ce2b1a6d-e550-0410-aec6-3dcde31c8c00