Store the event of settings db downgrade

bug:30561721

Change-Id: I8f2252bbf99603976c7efc32c54aa88b314ba815
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index e836143..068de5a 100755
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -8721,6 +8721,16 @@
         public static final String RETAIL_DEMO_MODE_CONSTANTS = "retail_demo_mode_constants";
 
         /**
+         * The reason for the settings database being downgraded. This is only for
+         * troubleshooting purposes and its value should not be interpreted in any way.
+         *
+         * Type: string
+         *
+         * @hide
+         */
+        public static final String DATABASE_DOWNGRADE_REASON = "database_downgrade_reason";
+
+        /**
          * Settings to backup. This is here so that it's in the same place as the settings
          * keys and easy to update.
          *