Adding RegisterDependantFieldTrial interface method.

components/sync/user_events/user_event_service.cc

 // Copyright 2017 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/user_events/user_event_service.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/feature_list.h"
 #include "base/memory/ptr_util.h"
 #include "base/rand_util.h"
 #include "components/sync/driver/sync_driver_switches.h"
 #include "components/sync/driver/sync_service.h"
 #include "components/sync/model/model_type_sync_bridge.h"
-#include "components/sync/protocol/sync.pb.h"
 #include "components/sync/user_events/user_event_sync_bridge.h"
 
 using sync_pb::UserEventSpecifics;
 
 namespace syncer {
 
-namespace {}  // namespace
-
 UserEventService::UserEventService(SyncService* sync_service,
                                    std::unique_ptr<UserEventSyncBridge> bridge)
     : sync_service_(sync_service),
       bridge_(std::move(bridge)),
-      session_id_(base::RandUint64()) {}
+      session_id_(base::RandUint64()) {
+  // TODO(skym): Subscribe to events about field trial membership changing.
+}
 
 UserEventService::~UserEventService() {}
 
 void UserEventService::Shutdown() {}
 
 void UserEventService::RecordUserEvent(
     std::unique_ptr<UserEventSpecifics> specifics) {
   if (CanRecordEvent(*specifics)) {
     DCHECK(!specifics->has_session_id());
     specifics->set_session_id(session_id_);
@@ skipping 11 matching lines @@
 
 bool UserEventService::CanRecordEvent(const UserEventSpecifics& specifics) {
   // We only record events if the user is syncing history and has not enabled
   // a custom passphrase. The type HISTORY_DELETE_DIRECTIVES is enabled in and
   // only in this exact scenario.
   return base::FeatureList::IsEnabled(switches::kSyncUserEvents) &&
          sync_service_ != nullptr && sync_service_->IsEngineInitialized() &&
          sync_service_->GetPreferredDataTypes().Has(HISTORY_DELETE_DIRECTIVES);
 }
 
+void RegisterDependentFieldTrial(const std::string& trial_name,
+                                 UserEventSpecifics::EventCase event_case) {
+  // TODO(skym): Implementation.
+}
+
 }  // namespace syncer