MIPS: Start using OStreams.

Port r22179 (01402bc)

Original commit message:
Note that until everything is OStream-based, there are a few places
where we have to do some impedance matching. A few accessors had to be
const-corrected on the way.

BUG=
R=palfia@homejinni.com

Review URL: https://codereview.chromium.org/369873002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22196 ce2b1a6d-e550-0410-aec6-3dcde31c8c00