title: Is it possible to use Firebase without variable project ID
body: <p>I am developing an Android App but have some specially requirements.</p>
  
  <p>I want to allow user to enter their own send_id and API_KEY, but all the guide google offered is to use the google-service.json and fixed id.</p>
  
  <p>I tried manually initial FirebaseApp instance but get null token from FirebaseInstanceID.</p>
  
  <p>So is this possible to manually initial Firebase and works as charm?</p>