This allows to distinguish between stubs compiled for the current object from
stubs compiled for objects that have the current object as a prototype.

BUG=v8:2593
R=verwaest@chromium.org

Review URL: https://chromiumcodereview.appspot.com/13552003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14132 ce2b1a6d-e550-0410-aec6-3dcde31c8c00