MIPS: Replace OStream with std::ostream.

Port r24319 (b4a085f)

BUG=
R=akos.palfi@imgtec.com

Review URL: https://codereview.chromium.org/615013002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24332 ce2b1a6d-e550-0410-aec6-3dcde31c8c00