[Sync] Add support for performing a GetKey on startup.

sync/internal_api/public/sessions/model_neutral_state.h

 // Copyright (c) 2012 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.
 
 #ifndef SYNC_SESSIONS_MODEL_NEUTRAL_STATE_H
 #define SYNC_SESSIONS_MODEL_NEUTRAL_STATE_H
 
 #include "base/basictypes.h"
 #include "sync/internal_api/public/util/syncer_error.h"
 #include "sync/protocol/sync.pb.h"
@@ skipping 30 matching lines @@
   // the client must now "migrate", by purging and re-downloading all updates.
   ModelTypeSet types_needing_local_migration;
 
   // Overwrites due to conflict resolution counters.
   int num_local_overwrites;
   int num_server_overwrites;
 
   // Any protocol errors that we received during this sync session.
   SyncProtocolError sync_protocol_error;
 
-  // Records the most recent results of PostCommit and GetUpdates commands.
+  // Records the most recent results of GetKey, PostCommit and GetUpdates
+  // commands.
+  SyncerError last_get_key_result;
   SyncerError last_download_updates_result;
   SyncerError commit_result;
 
   // Set to true by ResolveConflictsCommand if any forward progress was made.
   bool conflicts_resolved;
 
   // Set to true by PostCommitMessageCommand if any commits were successful.
   bool items_committed;
 
   // True indicates debug info has been sent once this session.
   bool debug_info_sent;
 
   // Number of changes remaining, according to the server.
   // Take it as an estimate unless it's value is zero, in which case there
   // really is nothing more to download.
   int64 num_server_changes_remaining;
 };
 
 }  // namespace sessions
 }  // namespace syncer
 
 #endif  // SYNC_SESSIONS_MODEL_NEUTRAL_STATE_H_