The previous CL used the wrong map in some cases, leading to a wrong decision
regarding monomorphic usage and therefore some performance regressions.

Review URL: https://chromiumcodereview.appspot.com/10694129

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12037 ce2b1a6d-e550-0410-aec6-3dcde31c8c00