Adding RegisterDependantFieldTrial interface method.

components/sync/user_events/user_event_service.h

 // 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.
 
 #ifndef COMPONENTS_SYNC_USER_EVENTS_USER_EVENT_SERVICE_H_
 #define COMPONENTS_SYNC_USER_EVENTS_USER_EVENT_SERVICE_H_
 
 #include <memory>
+#include <string>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "components/keyed_service/core/keyed_service.h"
-
-namespace sync_pb {
-class UserEventSpecifics;
-}  // namespace sync_pb
+#include "components/sync/protocol/user_event_specifics.pb.h"
 
 namespace syncer {
 
 class ModelTypeSyncBridge;
 class SyncService;
 class UserEventSyncBridge;
 
 class UserEventService : public KeyedService {
  public:
   UserEventService(SyncService* sync_service,
                    std::unique_ptr<UserEventSyncBridge> bridge);
 
   ~UserEventService() override;
 
   // KeyedService implementation
   void Shutdown() override;
 
   // Records a given event to be reported. Relevant settings will be checked to
   // verify user events should be emitted and this will no-op if the the
   // requisite permissions are not present.
   void RecordUserEvent(std::unique_ptr<sync_pb::UserEventSpecifics> specifics);
   void RecordUserEvent(const sync_pb::UserEventSpecifics& specifics);
 
+  // Register that knowledge about a given field trial is important when
+  // interpreting specified user event type, and should be recorded if assigned.
+  void RegisterDependentFieldTrial(
+      const std::string& trial_name,
+      sync_pb::UserEventSpecifics::EventCase event_case);
+
   base::WeakPtr<ModelTypeSyncBridge> GetSyncBridge();
 
  private:
   bool CanRecordEvent(const sync_pb::UserEventSpecifics& specifics);
 
   SyncService* sync_service_;
 
   std::unique_ptr<UserEventSyncBridge> bridge_;
 
   // Holds onto a random number for the duration of this execution of chrome. On
   // restart it will be regenerated. This can be attached to events to know
   // which events came from the same session.
   uint64_t session_id_;
 
   DISALLOW_COPY_AND_ASSIGN(UserEventService);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_USER_EVENTS_USER_EVENT_SERVICE_H_