Allow mediaextractor to load libraries from apk_data_file

This is an experimental feature only on userdebug and eng build.

Test: play MP4 file. install & uninstall media update apk.
Bug: 67908547
Change-Id: I513cdbfda962f00079e886b7a42f9928e81f6474
diff --git a/private/system_server.te b/private/system_server.te
index 035e8f1..6ebcab5 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -746,6 +746,11 @@
 allow system_server user_profile_data_file:dir { search };
 allow system_server user_profile_data_file:file { getattr open read };
 
+userdebug_or_eng(`
+  # Allow system server to notify mediaextractor of the plugin update.
+  allow system_server mediaextractor_update_service:service_manager find;
+')
+
 ###
 ### Neverallow rules
 ###