Add keystore permission for metrics re-routing.

Keystore2 atoms need to be rounted to statsd via a proxy.
The proxy needs to have this permission in order to pull metrics from
keystore.

Ignore-AOSP-First: No mergepath to AOSP.
Bug: 188590587
Test: Statsd Testdrive script
Change-Id: Ic94f4bb19a08b6300cfd2d3ed09b31d5b7081bfd
Merged-In: Ic94f4bb19a08b6300cfd2d3ed09b31d5b7081bfd
(cherry picked from commit 61d07e7ce067bbfee6a84f422e6c229382a1e4a1)
diff --git a/private/service_contexts b/private/service_contexts
index e6b88c2..f8c1607 100644
--- a/private/service_contexts
+++ b/private/service_contexts
@@ -39,6 +39,7 @@
 android.security.keystore                 u:object_r:keystore_service:s0
 android.security.legacykeystore           u:object_r:legacykeystore_service:s0
 android.security.maintenance              u:object_r:keystore_maintenance_service:s0
+android.security.metrics                  u:object_r:keystore_metrics_service:s0
 android.security.remoteprovisioning       u:object_r:remoteprovisioning_service:s0
 android.service.gatekeeper.IGateKeeperService    u:object_r:gatekeeper_service:s0
 app_binding                               u:object_r:app_binding_service:s0