Tag handlers as monomorphic

BUG=
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/444623002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22868 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Remove broken _WIN64 checks.

TBR=hpayer@chromium.org

Review URL: https://codereview.chromium.org/440863002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22869 ce2b1a6d-e550-0410-aec6-3dcde31c8c00