title: Firebase Cloud Messaging, in onRefreshToken, I can't access my preferences
body: <p>I'm testing Firebase Cloud Messaging under Android Sudio on Ubuntu after I have deleted my android app that implements it on my target phone.
  As explained in the documentation, onRefreshToken is called when I start the app for the first time. I try to send the token to my app server, whose URL is stored in the app's Preferences.</p>
  
  <p>Unfortunately I can't read the preferences until after onCreate runs, which is after the onRefreshToken runs. Thus I can't send the new token automatically to my server.</p>
  
  <p>How can I get round this , preferably by being able to read the preferences in the onRefreshToken callback?</p>