This makes sure that the DoubleToIStub::Generate method
does not overwrite the value of the f12 register.

TEST=bencnhmarks/kraken/stanford-crypto-pbkdf2
BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/33463002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17306 ce2b1a6d-e550-0410-aec6-3dcde31c8c00