microdroid: Add prop to wait for /data/tombstones

Bug: 266470759
Test: atest MicrodroidHostTestCases MicrodroidTestApp
Change-Id: Ie9992e105e57f1088a6016f0179c7dc3d285a7ed
diff --git a/microdroid/system/private/property_contexts b/microdroid/system/private/property_contexts
index d32e0e8..235ab14 100644
--- a/microdroid/system/private/property_contexts
+++ b/microdroid/system/private/property_contexts
@@ -163,3 +163,7 @@
 apexd.payload_metadata.path u:object_r:apexd_payload_metadata_prop:s0 exact string
 
 tombstone_transmit.init_done u:object_r:tombstone_transmit_status_prop:s0 exact bool
+
+# tombstone_transmit.start starts tombstone_transmit after creating a directory
+# assigning the same label as ctl.start$tombstone_transmit
+tombstone_transmit.start u:object_r:ctl_tombstone_transmit_prop:s0 exact bool