Add policy for 'debug.tracing.desktop_mode_visible_tasks' system
property

The property will be used to hold the number of visible windows when
in desktop mode. It will be written by com.android.systemui and
read by perfetto to set the initial value of a counter in traces.

Bug: 358369221
Test: Verified on device
Change-Id: Iad8dc7a66765856ee7affb707f2dba6c1bbfbf49
diff --git a/private/property_contexts b/private/property_contexts
index f0a4281..f631f8f 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -33,6 +33,7 @@
 
 debug.                  u:object_r:debug_prop:s0
 debug.db.               u:object_r:debuggerd_prop:s0
+debug.tracing.desktop_mode_visible_tasks u:object_r:debug_tracing_desktop_mode_visible_tasks_prop:s0 exact uint
 dumpstate.              u:object_r:dumpstate_prop:s0
 dumpstate.options       u:object_r:dumpstate_options_prop:s0
 init.svc_debug_pid.     u:object_r:init_svc_debug_prop:s0