Add typecast to fix compiling in MSVC

BUG=none
TEST=make && make runtests

Change-Id: I774645c1059df70cd25ea6a3f78161eb916d7293
Reviewed-on: http://gerrit.chromium.org/gerrit/4192
Reviewed-by: Stefan Reinauer <reinauer@google.com>
Tested-by: Randall Spangler <rspangler@chromium.org>
1 file changed