Improve reporting of bucketing reason

Keep track of main and sub reason for bucket change

Bug: 73178753
Test: atest AppIdleHistoryTests
Change-Id: I4936281ac06046bb5ffed9f3306efa24c7fd47ab
diff --git a/services/usage/java/com/android/server/usage/UserUsageStatsService.java b/services/usage/java/com/android/server/usage/UserUsageStatsService.java
index 8afc511..3fbcd81 100644
--- a/services/usage/java/com/android/server/usage/UserUsageStatsService.java
+++ b/services/usage/java/com/android/server/usage/UserUsageStatsService.java
@@ -520,7 +520,8 @@
             pw.printPair("shortcutId", event.mShortcutId);
         }
         if (event.mEventType == UsageEvents.Event.STANDBY_BUCKET_CHANGED) {
-            pw.printPair("standbyBucket", event.mBucket);
+            pw.printPair("standbyBucket", event.getStandbyBucket());
+            pw.printPair("reason", UsageStatsManager.reasonToString(event.getStandbyReason()));
         }
         pw.printHexPair("flags", event.mFlags);
         pw.println();