MIPS: Assign less environments.

Port r14983 (960d6de)

BUG=

Review URL: https://codereview.chromium.org/16567002
Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14988 ce2b1a6d-e550-0410-aec6-3dcde31c8c00