MediaTranscodingService: Add sepolicy for MediaTranscodingService.

Bug:145233472
Test: Build and flash the phone.
"adb shell dumpsys -l | grep media" shows media.transcoding service.

Change-Id: I48a42e7b595754989c92a8469eb91360ab6db7c6
diff --git a/private/file_contexts b/private/file_contexts
index 2ec5b2f..69b6c58 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -239,6 +239,7 @@
 /system/bin/cameraserver	u:object_r:cameraserver_exec:s0
 /system/bin/mediaextractor	u:object_r:mediaextractor_exec:s0
 /system/bin/mediaswcodec	u:object_r:mediaswcodec_exec:s0
+/system/bin/mediatranscoding	u:object_r:mediatranscoding_exec:s0
 /system/bin/mdnsd	u:object_r:mdnsd_exec:s0
 /system/bin/installd	u:object_r:installd_exec:s0
 /system/bin/otapreopt_chroot   u:object_r:otapreopt_chroot_exec:s0