X87: Introduce code stub constructors for stub keys.

port r23716.

original commit message:

  Introduce code stub constructors for stub keys.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/556653004

Patch from Jing Bao <jing.bao@intel.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23815 ce2b1a6d-e550-0410-aec6-3dcde31c8c00