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/platform_app.te b/private/platform_app.te
index eb1a7c7..320624c 100644
--- a/private/platform_app.te
+++ b/private/platform_app.te
@@ -51,6 +51,7 @@
 userdebug_or_eng(`
   set_prop(platform_app, persist_sysui_ranking_update_prop)
 ')
+set_prop(platform_app, debug_tracing_desktop_mode_visible_tasks_prop)
 
 # com.android.captiveportallogin reads /proc/vmstat
 allow platform_app {