SFTP File System provides you an ability to access to a SFTP server directly from the Files app.
Before building this, you have to install nacl-sdk and libssh2 from naclports.
$ git clone https://github.com/yoichiro/chromeos-filesystem-sftp.git
$ cd chromeos-filesystem-sftp
$ npm install
$ grunt
All files are licensed under the BSD license. See the LICENSE file for details. All original source code is Copyright 2015 Yoichiro Tanaka.