title: Firebase message not received on emulator
body: <p>I followed the instructions in <a href="https://stackoverflow.com/a/38626398/565212">https://stackoverflow.com/a/38626398/565212</a> to connect SNS to FCM to an Android app.
  When deployed to an emulator, the app initializes but does not receive any messages.
  The same app works correctly on my actual Nexus 6 device and receives messages.
  Why this difference?</p>