Check for messaging compatibility.

See firebase/firebase-js-sdk#1260

Author: muldoon2007

firebase-messaging-sw.js

@@ -4,7 +4,10 @@ importScripts('bower_components/firebase/firebase-messaging.js');
 firebase.initializeApp({
   messagingSenderId: '{$ firebase.messagingSenderId $}',
 });
-const messaging = firebase.messaging();
+
+if (firebase.messaging.isSupported()) {
+  const messaging = firebase.messaging();
+}
 
 messaging.setBackgroundMessageHandler(({ data }) => {
   const notification = Object.assign({}, data, {