Invoking cancellation callback in onCancelled()

We are reporting cancellations as failures (well, "not-received" callbacks). It is implicit in the callbacks interfaces, and reflected in code here.

What do you think about creating a method to the cancellation in the callbacks?

I know it may sound as more code, but it may be less code actually. For example, in the app, we only implement one method, but in that method we have code to distinguish a failure vs a cancellation.

Also, most APIs have a custom callback for cancellations.