[Sync] Ensure that CONFIGURE_CLEAN types get unapplied before configuration

components/sync/driver/glue/sync_backend_host_impl.cc

 // Copyright 2013 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.
 
 #include "components/sync/driver/glue/sync_backend_host_impl.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 263 matching lines @@
   // that the requested types list includes at least one non-nigori type.  It
   // will not send a MIGRATION_DONE response in that case.  We still need to be
   // careful to not send progress markers for non-nigori types, though.  If a
   // non-nigori type in the request requires migration, a MIGRATION_DONE
   // response will be sent.
 
   ModelSafeRoutingInfo routing_info;
   registrar_->GetModelSafeRoutingInfo(&routing_info);
 
   ModelTypeSet current_types = registrar_->GetLastConfiguredTypes();
-  ModelTypeSet types_to_purge = Difference(ModelTypeSet::All(), current_types);
+  ModelTypeSet types_to_purge = Difference(
+      ModelTypeSet::All(), Difference(current_types, clean_first_types));

[Nicolas Zea, 2016/12/16 22:08:42]

I think it might be simpler to understand if we just insert clean_first_types
into types_to_purge?

[pavely, 2016/12/16 23:57:46]

Done.

   ModelTypeSet inactive_types =
       GetDataTypesInState(CONFIGURE_INACTIVE, config_state_map);
   types_to_purge.RemoveAll(inactive_types);
   types_to_purge.RemoveAll(unready_types);
 
   // If a type has already been disabled and unapplied or journaled, it will
   // not be part of the |types_to_purge| set, and therefore does not need
   // to be acted on again.
   fatal_types.RetainAll(types_to_purge);
   ModelTypeSet unapply_types = Union(crypto_types, clean_first_types);
@@ skipping 400 matching lines @@
     const SyncManager::ClearServerDataCallback& frontend_callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
   frontend_callback.Run();
 }
 
 }  // namespace syncer
 
 #undef SDVLOG
 
 #undef SLOG