I know about file system api exposed to native client but it seems it can not allow access outside sandbox. There is an api which can allow access outside sandbox by a prompt window.
If my understanding is correct it can not allow access to a directory. I recently came across chrome dev which allow you to create workspace in any directory and allows cut, copy and paste operations even at directory level. I am wondering how are they getting the access to files and directory outside sandbox.
The extension which I am referring is: https://github.com/dart-lang/chromedeveditor