Right now we look up the correct channel ID for a web notification based on its origin, by iterating through all site channels and finding the one which matches the notification's origin, after the JNI call to NotificationPlatformBridge.displayNotification has come through.

In order for the NotificationPlatformBridge framework to be generalized for non-web notifications, we'll need to start passing through the channel ID alongside the other notification properties in the displayNotification call.

More notes here:
https://docs.google.com/a/google.com/document/d/15opNtE_SQuWnF14PFFx46XHMzzEitzPQtOrhd3wdPs8/edit?usp=sharing