[Sync] Renaming client key to client tag.

sync/api/entity_change.h

 // 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.
 
 #ifndef SYNC_API_ENTITY_CHANGE_H_
 #define SYNC_API_ENTITY_CHANGE_H_
 
 #include <string>
 #include <vector>
 
 #include "sync/api/entity_data.h"
 #include "sync/base/sync_export.h"
 
 namespace syncer_v2 {
 
 class SYNC_EXPORT EntityChange {
  public:
   enum ChangeType {
     ACTION_ADD,
     ACTION_UPDATE,
     ACTION_DELETE
   };
 
-  static EntityChange CreateAdd(std::string client_key, EntityDataPtr data);
-  static EntityChange CreateUpdate(std::string client_key, EntityDataPtr data);
-  static EntityChange CreateDelete(std::string client_key);
+  static EntityChange CreateAdd(std::string client_tag, EntityDataPtr data);
+  static EntityChange CreateUpdate(std::string client_tag, EntityDataPtr data);
+  static EntityChange CreateDelete(std::string client_tag);
 
   virtual ~EntityChange();
 
-  std::string client_key() const { return client_key_; }
+  std::string client_tag() const { return client_tag_; }
   ChangeType type() const { return type_; }
   const EntityData& data() const { return data_.value(); }
 
  private:
-  EntityChange(std::string client_key, ChangeType type, EntityDataPtr data);
+  EntityChange(std::string client_tag, ChangeType type, EntityDataPtr data);
 
-  std::string client_key_;
+  std::string client_tag_;
   ChangeType type_;
   EntityDataPtr data_;
 };
 
 typedef std::vector<EntityChange> EntityChangeList;
 
 }  // namespace syncer_v2
 
 #endif  // SYNC_API_ENTITY_CHANGE_H_