make_conf_util: Include chromeos-partner-overlay in PORTDIR_OVERLAY.

We are introducing private SDK packages in chromeos-partner-overlay.

BUG=chromium:890672
TEST=./update_chroot
TEST=portageq envvar PORTDIR_OVERLAY

Change-Id: Ia700a58d3ec7dd919c0522b13ad6d94365d582a7
Reviewed-on: https://chromium-review.googlesource.com/1307277
Commit-Ready: Shuhei Takahashi <nya@chromium.org>
Tested-by: Shuhei Takahashi <nya@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/sdk_lib/make_conf_util.sh b/sdk_lib/make_conf_util.sh
index e6ea796..e687dd3 100644
--- a/sdk_lib/make_conf_util.sh
+++ b/sdk_lib/make_conf_util.sh
@@ -78,9 +78,15 @@
     echo 'RESUMECOMMAND_GS="${FETCHCOMMAND_GS}"'
   fi
 
-  if [[ -d "${chromeos_overlay}" ]]; then
-    echo "PORTDIR_OVERLAY=\"\$PORTDIR_OVERLAY ${chromeos_overlay}\""
-  fi
+  local chromeos_partner_overlay="src/private-overlays/chromeos-partner-overlay"
+  chromeos_partner_overlay="${CHROOT_TRUNK_DIR}/${chromeos_partner_overlay}"
+
+  local overlay
+  for overlay in "${chromeos_partner_overlay}" "${chromeos_overlay}"; do
+    if [[ -d "${overlay}" ]]; then
+      echo "PORTDIR_OVERLAY=\"\$PORTDIR_OVERLAY ${overlay}\""
+    fi
+  done
 }
 
 # Create /etc/make.conf.host_setup according to parameters.