Add unistd.h to make gcc 4.7 can compile

BUG=None
TEST=compile pass

Change-Id: I6353902cbdffc3397b5c5a3eafac667481514bbf
Reviewed-on: https://gerrit.chromium.org/gerrit/21649
Reviewed-by: <tbarzic@google.com>
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Reviewed-by: Yunlian Jiang <yunlian@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
Commit-Ready: Yunlian Jiang <yunlian@chromium.org>
1 file changed