error seeking persistent file permission

[tejkweku]

I do get the error below when I try to seek permission for reading/writing persistent files in Chrome Version 64.0.3282.167 (Official Build) on windows.
filer.js:453 Uncaught TypeError: self.requestFileSystem is not a function at Filer.<anonymous> (filer.js:453) (anonymous) @ filer.js:453
It works when I change the function to be invoked from self.requestFileSystem to window.requestFileSystem