Informs GDK that the drop ended.
Passing false for success may trigger a drag cancellation animation.
This function is called by the drag source, and should be the last call before dropping the reference to the this.
The `GdkDrag` will only take the first [[email protected]_done] call as effective, if this function is called multiple times, all subsequent calls will be ignored.
| this |
a `GdkDrag` |
| success |
whether the drag was ultimatively successful |