[Sync] Create UserEventService.

chrome/browser/sync/user_event_service_factory.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 CHROME_BROWSER_SYNC_USER_EVENT_SERVICE_FACTORY_H_
+#define CHROME_BROWSER_SYNC_USER_EVENT_SERVICE_FACTORY_H_
+
+#include "base/macros.h"
+#include "base/memory/singleton.h"
+#include "components/keyed_service/content/browser_context_keyed_service_factory.h"
+
+class Profile;
+
+namespace syncer {
+class UserEventService;
+}  // namespace syncer
+
+namespace browser_sync {
+
+// Factory for BrowserKeyedService UserEventService.

[Patrick Noland, 2017/05/08 22:42:37]

Maybe this is c/p boilerplate, but I don't think this comment adds much

[skym, 2017/05/08 23:35:27]

Done.

+class UserEventServiceFactory : public BrowserContextKeyedServiceFactory {
+ public:
+  static syncer::UserEventService* GetForProfile(Profile* profile);
+  static UserEventServiceFactory* GetInstance();
+
+ private:
+  friend struct base::DefaultSingletonTraits<UserEventServiceFactory>;
+
+  UserEventServiceFactory();
+  ~UserEventServiceFactory() override;
+
+  // BrowserContextKeyedServiceFactory:
+  KeyedService* BuildServiceInstanceFor(
+      content::BrowserContext* context) const override;
+
+  DISALLOW_COPY_AND_ASSIGN(UserEventServiceFactory);
+};
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_USER_EVENT_SERVICE_FACTORY_H_