MIPS: Implement inline %_IsJSProxy() for full codegen and Hydrogen.

Port r24636

Original commit message:
Saving a runtime call for many builtin functions.

BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/661503002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24645 ce2b1a6d-e550-0410-aec6-3dcde31c8c00