Add new "procrank" SELinux domain.

/system/xbin/procrank is a setuid program run by adb shell on
userdebug / eng devices. Allow it to work without running adb root.

Bug: 18342188
Change-Id: I18d9f743e5588c26661eaa26e1b7e6980b15caf7
diff --git a/file_contexts b/file_contexts
index ce55cc8..27d5842 100644
--- a/file_contexts
+++ b/file_contexts
@@ -156,6 +156,7 @@
 /system/bin/tf_daemon	u:object_r:tee_exec:s0
 /system/bin/racoon	u:object_r:racoon_exec:s0
 /system/xbin/su		u:object_r:su_exec:s0
+/system/xbin/procrank   u:object_r:procrank_exec:s0
 /system/vendor/bin/gpsd u:object_r:gpsd_exec:s0
 /system/bin/dnsmasq     u:object_r:dnsmasq_exec:s0
 /system/bin/hostapd     u:object_r:hostapd_exec:s0