Add typing for Int32MulHigh.

TBR=rossberg@chromium.org
BUG=

Review URL: https://codereview.chromium.org/656803003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24602 ce2b1a6d-e550-0410-aec6-3dcde31c8c00