[Sync] Add support for retrying a getupdates due to a context change

sync/engine/get_updates_processor.h

 // Copyright 2014 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_ENGINE_GET_UPDATES_PROCESSOR_H
 #define SYNC_ENGINE_GET_UPDATES_PROCESSOR_H
 
 #include <map>
 #include <vector>
 
@@ skipping 64 matching lines @@
                                      sessions::SyncSession* session,
                                      sync_pb::ClientToServerMessage* msg);
 
   // Helper function for processing responses from the server.  Defined here for
   // testing.
   SyncerError ProcessResponse(const sync_pb::GetUpdatesResponse& gu_response,
                               ModelTypeSet proto_request_types,
                               sessions::StatusController* status);
 
   // Processes a GetUpdates responses for each type.
-  bool ProcessGetUpdatesResponse(
+  syncer::SyncerError ProcessGetUpdatesResponse(
       ModelTypeSet gu_types,
       const sync_pb::GetUpdatesResponse& gu_response,
       sessions::StatusController* status_controller);
 
   static void CopyClientDebugInfo(
       sessions::DebugInfoGetter* debug_info_getter,
       sync_pb::DebugInfo* debug_info);
 
   FRIEND_TEST_ALL_PREFIXES(GetUpdatesProcessorTest, BookmarkNudge);
   FRIEND_TEST_ALL_PREFIXES(GetUpdatesProcessorTest, NotifyMany);
@@ skipping 14 matching lines @@
   UpdateHandlerMap* update_handler_map_;
 
   const GetUpdatesDelegate& delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(GetUpdatesProcessor);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_GET_UPDATES_PROCESSOR_H_