De-virtualize GenerateNameCheck.

Currently there are two kinds of "vtables" used in the load/store stub
compilers: kind() and C++'s own vtables. This is a bit confusing, and
this is a step towards simplifying things.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/141763002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18676 ce2b1a6d-e550-0410-aec6-3dcde31c8c00