title: Notification Service Extension does not handle data messages when using Firebase Data Message
body: <p>The app is on both iOS and Android, for this notification to work on both platforms, I removed <code>notification</code> field from notification json payload. But now iOS does not handle this notification when in background.</p>
  
  <p>This one works on iOS but it has <code>notification</code> field which I do <strong>not</strong> want.</p>
  
  <pre><code>{
    "registration_ids": [
          "...",
          "..."
      ],
    "priority": "high",
    "notification": {
      "body": "Notification Body.",
      "title": "Notification Title"
    },
    "data": {
      "userId": "11111",
      "badge": 10
    }
  }
  </code></pre>
  
  <p>This one works in android but <strong>not</strong> working on iOS when in background:</p>
  
  <pre><code>{
    "registration_ids": [
          "...",
          "..."
      ],
    "mutable_content": true,
    "content_available": true,
    "data": {
      "click_action": "AndroidIntent"
      "message": "Notification Body",
      "myDataField": "11",
      "location": "3",
      "imageurl": "http://image.com/13fd.png"
    }
  }
  </code></pre>
  
  <p>The bottom one does not even enter my Notification Service Extension. How do I make sure my Notification Service Extension is called without adding a <code>notification</code> field on my json?</p>