Add missing include.

libc++ used to leak unistd.h from every headers. This is fixed in the
latest version.

The code that needs this is not upstream code
(https://googleplex-android-review.git.corp.google.com/#/c/645357/),
so no need to send upstream.

Change-Id: I51111c08b4d2620a5d264e20646e6606a3f39c7e
(cherry picked from commit 8fc83651c5d7c5bc7413be76f82df0b23c681313)
1 file changed