xsrf token sometimes needs to be reloaded

[simon-weber]

So I had suspected this as a problem for a while, but I hadn't confirmed it until now, when I accidentally recreated it on my account.

streamingloadalltracks turned out to be the key, since it actually sends back json. I was getting back:

{"success":false, "reloadXsrf": true}

Sure enough, the xt cookie had been changed.

We'll need to have the background script detect this and send a message to the content script to retrieve it. I confirmed that window._GU_getCookie('xt') returns the new token.