Ported r8238 (7803ed7)

This commit would have also included changes to macro-assembler-mips.cc,
however Kevin M. did those changes in later commit r8248. (thx!)

BUG=
TEST=

Review URL: http://codereview.chromium.org//6995128
Patch from Paul Lind <plind44@gmail.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8249 ce2b1a6d-e550-0410-aec6-3dcde31c8c00