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

components/sync/user_events/user_event_service_impl.h

Index: components/sync/user_events/user_event_service_impl.h
diff --git a/components/sync/user_events/user_event_service_impl.h b/components/sync/user_events/user_event_service_impl.h
new file mode 100644
index 0000000000000000000000000000000000000000..578543f911976d722f13776db185f22086a27e5d
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+++ b/components/sync/user_events/user_event_service_impl.h
@@ -0,0 +1,58 @@
+// 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_IMPL_H_
+#define COMPONENTS_SYNC_USER_EVENTS_USER_EVENT_SERVICE_IMPL_H_
+
+#include <memory>
+#include <string>
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "components/keyed_service/core/keyed_service.h"
+#include "components/sync/protocol/user_event_specifics.pb.h"
+#include "components/sync/user_events/user_event_service.h"
+
+namespace syncer {
+
+class ModelTypeSyncBridge;
+class SyncService;
+class UserEventSyncBridge;
+
+class UserEventServiceImpl : public UserEventService {
+ public:
+  UserEventServiceImpl(SyncService* sync_service,
+                       std::unique_ptr<UserEventSyncBridge> bridge);
+  ~UserEventServiceImpl() override;
+
+  // KeyedService implementation.
+  void Shutdown() override;
+
+  // UserEventService implementation.
+  void RecordUserEvent(
+      std::unique_ptr<sync_pb::UserEventSpecifics> specifics) override;
+  void RecordUserEvent(const sync_pb::UserEventSpecifics& specifics) override;
+  void RegisterDependentFieldTrial(
+      const std::string& trial_name,
+      sync_pb::UserEventSpecifics::EventCase event_case) override;
+  base::WeakPtr<ModelTypeSyncBridge> GetSyncBridge() override;
+
+ private:
+  bool ShouldRecordEvent(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(UserEventServiceImpl);
+};
+
+}  // namespace syncer
+
+#endif  // COMPONENTS_SYNC_USER_EVENTS_USER_EVENT_SERVICE_IMPL_H_