MIPS: Turn the load field code stub into a hydrogen code stub.

Port r14526 (7c581932)

BUG=

Review URL: https://codereview.chromium.org/14855008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14529 ce2b1a6d-e550-0410-aec6-3dcde31c8c00