Increase pretenure ratio from 60% to 85%

As pretenure-call-new comes online, this is a better performing ratio
overall.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/196383032

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20041 ce2b1a6d-e550-0410-aec6-3dcde31c8c00