Chromium change:

https://chromium.googlesource.com/chromium/src/+/a76a6e39300b764f4a0e3824b9d17e6c2bf51b73

commit a76a6e39300b764f4a0e3824b9d17e6c2bf51b73
Author: Alex Chau <alexchau@chromium.org>
Date:   Wed Jun 26 16:20:01 2019 +0000

    Create WebPushSender for sending web-push messages

    - Created WebPushSender for sending out web-push messages using VAPID
      (https://developers.google.com/web/ilt/pwa/introduction-to-push-notifications#using_vapid)
    - Created WebPushMessage struct to encapsulate message_id into messages
      to make callbacks easier
    - Refactored across GCMEncryptionProvider / GCMDriver to use
      WebPushMessage and provide callback mechanism

    Bug: 966037