[Autofill] Add new API for getting FillEventHistory

Introduce a new callback in AutofillService that is called when the
session is finished.

Bug: 370059095
Test: android.autofillservice.cts.commontests.FillEventHistoryCommonTestCase.test_onSessionDestroyed
Flag: android.service.autofill.autofill_session_destroyed
Change-Id: I2fcb7d7a1a5c55e4afec73acd37a4bf148f3040b
diff --git a/services/autofill/features.aconfig b/services/autofill/features.aconfig
index 444844121..80ccb03 100644
--- a/services/autofill/features.aconfig
+++ b/services/autofill/features.aconfig
@@ -2,6 +2,13 @@
 container: "system"
 
 flag {
+  name: "autofill_session_destroyed"
+  namespace: "autofill"
+  description: "Guards against new metrics definitions introduced in W"
+  bug: "342676602"
+}
+
+flag {
   name: "autofill_w_metrics"
   namespace: "autofill"
   description: "Guards against new metrics definitions introduced in W"