Add default inbox field to settings.

Change-Id: I766c88c04efe889cb86d60d9fa5e03397d5dc7a5
diff --git a/src/com/android/mail/providers/UIProvider.java b/src/com/android/mail/providers/UIProvider.java
index cccafce..8908c5d 100644
--- a/src/com/android/mail/providers/UIProvider.java
+++ b/src/com/android/mail/providers/UIProvider.java
@@ -853,6 +853,7 @@
             SettingsColumns.CONFIRM_DELETE,
             SettingsColumns.CONFIRM_ARCHIVE,
             SettingsColumns.CONFIRM_SEND,
+            SettingsColumns.DEFAULT_INBOX
     };
 
     public static final class AutoAdvance {
@@ -938,5 +939,9 @@
          * be shown when a send action is performed.
          */
         public static final String CONFIRM_SEND = "confirm_send";
+        /**
+         * String folder containing the serialized default inbox folder for an account.
+         */
+        public static final String DEFAULT_INBOX = "default_inbox";
     }
 }