Merged r16596 into trunk branch.

MIPS: thread isolate for HConstant::handle.

R=yangguo@chromium.org
BUG=

Review URL: https://codereview.chromium.org/23766017

git-svn-id: https://v8.googlecode.com/svn/trunk@16625 ce2b1a6d-e550-0410-aec6-3dcde31c8c00