MIPS: port Refactor platform-specific code for determining shared stub for keyed load/stores.
MIPS: port Refactor platform-specific code for determining shared stub for keyed load/stores.

Ported r8253 (9d8e6ab).

BUG=
TEST=

Review URL: http://codereview.chromium.org//7003141
Patch from Paul Lind <plind44@gmail.com>.

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@8272 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh