Server directed error handling backend code.

chrome/browser/sync/protocol/sync.proto

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Sync protocol for communication between sync client and server.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 609 matching lines @@
                               // timeout). Client should try again later.
     MIGRATION_DONE     = 9;   // Migration has finished for one or more data
                               // types.  Client should clear the cache for
                               // these data types only and then re-sync with
                               // a server.
     UNKNOWN            = 100; // Unknown value. This should never be explicitly
                               // used; it is the default value when an
                               // out-of-date client parses a value it doesn't
                               // recognize.
   }
+
+  message Error {
+    optional ErrorType error_type       = 1 [default = UNKNOWN];
+    optional string error_description   = 2;
+    optional string url                 = 3;
+    enum Action {
+      UPGRADE_CLIENT              = 0; // Upgrade the client to latest version.
+      CLEAR_USER_DATA_AND_RESYNC  = 1; // Clear user data from dashboard and
+                                       // setup sync again.
+      ENABLE_SYNC_ON_ACCOUNT      = 2; // The administrator needs to enable sync
+                                       // on the account.
+      STOP_AND_RESTART_SYNC       = 3; // Stop sync and set up sync again.
+      DISABLE_SYNC_ON_CLIENT      = 4; // Wipe the client of all sync data and
+                                       // stop syncing.
+      UNKNOWN_ACTION              = 5; // This is the default.
+    }
+    optional Action action              = 4 [default = UNKNOWN_ACTION];
+  }
+
+  optional Error error = 13;
+
   // Up until protocol_version 24, the default was SUCCESS which made it
   // impossible to add new enum values since older clients would parse any
   // out-of-range value as SUCCESS. Starting with 25, unless explicitly set,
   // the error_code will be UNKNOWN so that clients know when they're
   // out-of-date. Note also that when using protocol_version < 25,
   // TRANSIENT_ERROR is not supported. Instead, the server sends back a HTTP
-  // 400 error code.
+  // 400 error code. This is deprecated now.
   optional ErrorType error_code = 4 [default = UNKNOWN];
   optional string error_message = 5;
 
   // Opaque store ID; if it changes, the contents of the client's cache
   // is meaningless to this server.  This happens most typically when
   // you switch from one storage backend instance (say, a test instance)
   // to another (say, the official instance).
   optional string store_birthday = 6;
 
   optional ClientCommand client_command = 7;
   optional ProfilingData profiling_data = 8;
 
   // The data types whose storage has been migrated.  Present when the value of
   // error_code is MIGRATION_DONE.
   repeated int32 migrated_data_type_id = 12;
 };