MIPS: thread isolate for files starting with 'b' and 'c'.

Port r16489 (bde75fe)

BUG=

Review URL: https://codereview.chromium.org/23814003
Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16498 ce2b1a6d-e550-0410-aec6-3dcde31c8c00