addTileCallback(callback) {
    return /** @type {!Object} */ (goog.events.listen(
        this,
        earthengine_api.javascript.abstractoverlay
            .AbstractOverlay.EventType.TILE_LOADED,
        callback));
  }
Adds a callback to be fired each time a tile is loaded.
@param {function(!earthengine_api.javascript.abstractoverlay.TileEvent)}
    callback The function to call when a tile has loaded.
@return {!Object} An ID which can be passed to removeTileCallback() to
    remove the callback.
@export