Initializes any callbacks for streams which have defined
        the plotted object as a source.

def _construct_callbacks(self):
        """
        Initializes any callbacks for streams which have defined
        the plotted object as a source.
        """
        cb_classes = set()
        registry = list(Stream.registry.items())
        callbacks = Stream._callbacks['bokeh']
        for source in self.link_sources:
            streams = [
                s for src, streams in registry for s in streams
                if src is source or (src._plot_id is not None and
                                     src._plot_id == source._plot_id)]
            cb_classes |= {(callbacks[type(stream)], stream) for stream in streams
                           if type(stream) in callbacks and stream.linked
                           and stream.source is not None}
        cbs = []
        sorted_cbs = sorted(cb_classes, key=lambda x: id(x[0]))
        for cb, group in groupby(sorted_cbs, lambda x: x[0]):
            cb_streams = [s for _, s in group]
            cbs.append(cb(self, cb_streams, source))
        return cbs