[Sync] USS: Add EntityChange.

sync/api/entity_change.cc

+// Copyright 2015 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 "sync/api/entity_change.h"
+
+namespace syncer_v2 {
+
+// static
+EntityChange EntityChange::CreateAdd(std::string client_tag,
+                                     EntityDataPtr data) {
+  return EntityChange(client_tag, ACTION_ADD, data);
+}
+
+// static
+EntityChange EntityChange::CreateUpdate(std::string client_tag,
+                                        EntityDataPtr data) {
+  return EntityChange(client_tag, ACTION_UPDATE, data);
+}
+
+// static
+EntityChange EntityChange::CreateDelete(std::string client_tag) {
+  return EntityChange(client_tag, ACTION_DELETE, EntityDataPtr());
+}
+
+EntityChange::EntityChange(std::string client_tag,
+                           ChangeType type,
+                           EntityDataPtr data)
+    : client_tag_(client_tag), type_(type), data_(data){};
+
+EntityChange::~EntityChange() {}
+
+}  // namespace syncer_v2