[Sync] Split UserEventService into interface and impl, add fake impl, add unit tests.

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/user_events/user_event_sync_bridge.h"
-
-using sync_pb::UserEventSpecifics;
-
 namespace syncer {
 
-UserEventService::UserEventService(SyncService* sync_service,
-                                   std::unique_ptr<UserEventSyncBridge> bridge)
-    : sync_service_(sync_service),
-      bridge_(std::move(bridge)),
-      session_id_(base::RandUint64()) {
-  // TODO(skym): Subscribe to events about field trial membership changing.
-}
+UserEventService::UserEventService() {}
 
 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_);
-    bridge_->RecordUserEvent(std::move(specifics));
-  }
-}
-
-void UserEventService::RecordUserEvent(const UserEventSpecifics& specifics) {
-  RecordUserEvent(base::MakeUnique<UserEventSpecifics>(specifics));
-}
-
-base::WeakPtr<ModelTypeSyncBridge> UserEventService::GetSyncBridge() {
-  return bridge_->AsWeakPtr();
-}
-
-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