Chromium's GCM Driver supports two kinds of subscriptions: GCM ("v3") and InstanceID. The Firebase team has just announced that the v3 registrations have been deprecated, and that the associated services will be turned off in April 2019.

https://developers.google.com/cloud-messaging/faq

Various Chromium features and third party developers (through extensions) depend on these subscriptions and will have to update. I'll file tracking bugs for those.

** Q: Is my feature affected?
You're affected when you use GCMDriver::Register(), GCMDriver::Unregister() and/or GCMDriver::UnregisterWithSenderId().

** Q: What should be used instead?
Get the InstanceIDDriver from the InstanceIDProfileService and get an InstanceID for your |app_id|. Here you can get and delete tokens, which is analogous to the Register/Unregister* methods on the GCM Driver.

** Q: Will existing subscriptions stop working?
Yes. Please provide an upgrade path migrating existing subscriptions to InstanceID ones. Both types of subscriptions are accepted by the server when sending a message.