Setup infrastructure (multi-db support) for the new grid migration algorithm

We'll have a db for each grid option and a db for back up / restore.

TODO(pinyaoting): support back up / restore using the new infrastructure, particularly calls to GridBackupTable should use different DBs when the feature flag (NEW_GRID_MIGRATION_ALGORITHM) is on.

Bug: 144052802
Test: N/A

Change-Id: I644a3e70148bd78204a747a337446a3c038f616f
diff --git a/src/com/android/launcher3/LauncherSettings.java b/src/com/android/launcher3/LauncherSettings.java
index 4c5c61c..49831f6 100644
--- a/src/com/android/launcher3/LauncherSettings.java
+++ b/src/com/android/launcher3/LauncherSettings.java
@@ -302,6 +302,8 @@
 
         public static final String METHOD_RESTORE_BACKUP_TABLE = "restore_backup_table";
 
+        public static final String METHOD_UPDATE_CURRENT_OPEN_HELPER = "update_current_open_helper";
+
         public static final String EXTRA_VALUE = "value";
 
         public static Bundle call(ContentResolver cr, String method) {