How implementable is NotificationAction.icon?

[saschanaz]

What is the issue with the Notifications API Standard?

It seems the only working implementation as of now is Chrome for Windows.

1. Windows: The action schema allows assigning an image via URL.
2. macOS: UNNotificationActionIcon only allows either the system icon or the app-bundled image, but not a random generated resource.
3. Linux: "actions-icons" hint is available but this replaces action text per the spec.
4. Android: Setting icon is possible, but the doc says "As of Android Build.VERSION_CODES.N, action button icons will not be displayed on action buttons"

If the only supported platform is Windows, maybe we should reconsider the inclusion of the feature in the spec.