It works great, and the design is minimally intrusive; thank you for making this.

Two suggestions: add a cancel button to cancel the deletion after it has begun, and show how many chats are yet to be deleted ("x of y deleted" or "x remaining").

And, as an added bonus, you could include the estimated time remaining. I just deleted 59 chats with this and every chat seemed to have a consistent amount of time required for deletion (about three seconds per chat). So a little "time remaining" bar shouldn't be difficult to implement.

And also a little chime (toggle-able on/off) would be nice to let the user know when the act is finished.

But simple and effective overall.