Add SELinux settings to support tracing during boot.

This CL adds the SELinux settings required to support tracing
during boot.
https://android-review.googlesource.com/#/c/157163/

BUG: 21739901
Change-Id: Ib3a7107776141ac8cf4f1ca06674f47a0d4b6ae0
diff --git a/property_contexts b/property_contexts
index 1844910..1583988 100644
--- a/property_contexts
+++ b/property_contexts
@@ -34,6 +34,7 @@
 service.adb.tcp.port    u:object_r:shell_prop:s0
 
 persist.audio.          u:object_r:audio_prop:s0
+persist.debug.          u:object_r:persist_debug_prop:s0
 persist.logd.           u:object_r:logd_prop:s0
 persist.sys.            u:object_r:system_prop:s0
 persist.service.        u:object_r:system_prop:s0