FYI I have added the `Token` class and `EditSession.getTokenAt` in edb16cc9e43ce7cc0b36a87841ff47801db73f1b.

Perhaps you may want to change the ace.js extension to only stream the `position` if that is all the data you need?  The receiver of the event can call `getTokenAt` if they need the token?  Or if you always need the token then introduce a `LinkEvent` to encapsulate the two.

Either way is fine for me, I would just like the dart event to carry the same data as the javascript.