[PATCH wayland] protocol: Improve data source notification around DnD progress

[Michael Catanzaro]

On Thu, 2015-10-29 at 16:37 +0800, Jonas Ådahl wrote:
> Correct me if I'm wrong, but this event is meant to be sent after a
> destination has read all the data it needs, meaning we could
> effectively
> send this for regular clipboard sources as well? Then just call it
> "finished".

I don't think we want the clipboard source to be simultaneously
canceled and finished. The events would be redundant, and canceled is
enough.