Allow PDF.js access to filesystem

[bsclifton]

The chromium extension PDF.js exposes a config option "Allow access to filesystem", which is defaulted to false. This prevents us from being able to open local PDFs

This issue would be either:

• defaulting the option to true
  OR
• exposing a way in the UI to toggle and defaulting to false

[diracdeltas]

duplicate of #2714

IIRC @willy-b looked into this and found it may not only be an issue of setting the permission

[diracdeltas]

i would suggest working on this after brave/pdf.js#2 is merged, since that PR does a lot of cleanup and removal of code that isn't needed in brave

[bsclifton]

@diracdeltas good catch :) I'll close this as a dupe During our triage meeting, @bbondy volunteered to look at it for our next release