FYI: Control Data + Per-Device Metadata

sync/sessions/sync_session.cc

 // 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.
 
 #include "sync/sessions/sync_session.h"
 
 #include <algorithm>
 #include <iterator>
 
 #include "base/logging.h"
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/internal_api/public/engine/model_safe_worker.h"
 #include "sync/syncable/directory.h"
 
 namespace syncer {
 namespace sessions {
 
 namespace {
 
 std::set<ModelSafeGroup> ComputeEnabledGroups(
     const ModelSafeRoutingInfo& routing_info,
     const std::vector<ModelSafeWorker*>& workers) {
   std::set<ModelSafeGroup> enabled_groups;
   // Project the list of enabled types (i.e., types in the routing
   // info) to a list of enabled groups.
   for (ModelSafeRoutingInfo::const_iterator it = routing_info.begin();
        it != routing_info.end(); ++it) {
     enabled_groups.insert(it->second);
   }
-  // GROUP_PASSIVE is always enabled, since that's the group that
-  // top-level folders map to.
+  // GROUP_PASSIVE is always enabled, since that's the group that top-level
+  // folders map to.
+  // GROUP_CONTROL manages some meta-data types that are always enabled.
   enabled_groups.insert(GROUP_PASSIVE);
+  enabled_groups.insert(GROUP_CONTROL);
   if (DCHECK_IS_ON()) {
     // We sometimes create dummy SyncSession objects (see
     // SyncScheduler::InitialSnapshot) so don't check in that case.
     if (!routing_info.empty() || !workers.empty()) {
       std::set<ModelSafeGroup> groups_with_workers;
       for (std::vector<ModelSafeWorker*>::const_iterator it = workers.begin();
            it != workers.end(); ++it) {
         groups_with_workers.insert((*it)->GetModelSafeGroup());
       }
       // All enabled groups should have a corresponding worker.
@@ skipping 226 matching lines @@
   // with the server. Therefore, we verify no errors and at least one SYNCER_OK.
   return reached_server && !HadErrors(state);
 }
 
 void SyncSession::SetFinished() {
   finished_ = true;
 }
 
 }  // namespace sessions
 }  // namespace syncer