I use DropBox (dropbox.com) Depending on how much data you want to sync, it is either free or a monthly charge. Up to 2 GB is free. I use it not only to sync (or backup, if you like) data on my Chromebook, but to sync collaborative items between my Chrombook, my desktop PC, my laptop, my wife's desktop and laptop and her executive assistant. In fact, I only download files from DropBox if I will need them when off-line.
The upload process requires that you use the "Basic loader". I assume the default loader is probably Java based and doesn't work. I don't know what difference it makes, the basic loader does the simple job that needs to be done.
The upload process requires that you use the "Basic loader". I assume the default loader is probably Java based and doesn't work. I don't know what difference it makes, the basic loader does the simple job that needs to be done.