Add constant for storing market backup state in shared preferences.

core/java/android/provider/Settings.java

@@ -2991,6 +2991,12 @@ public final class Settings {
         public static final String VENDING_REQUIRE_SIM_FOR_PURCHASE =
                 "vending_require_sim_for_purchase";
 
+        /**
+         * Indicates the Vending Machine backup state. It is set if the
+         * Vending application has been backed up at least once.
+         */
+        public static final String VENDING_BACKUP_STATE = "vending_backup_state";
+
         /**
          * The current version id of the Vending Machine terms of service.
          */