static cancel(tile) {
        if (tile) {
            tile.canceled = true;
            if (tile.source_data && tile.source_data.request_id) {
                Utils.cancelRequest(tile.source_data.request_id); // cancel pending tile network request
                tile.source_data.request_id = null;
            }

            Tile.abortBuild(tile);
        }
    }
Called on worker to cancel loading
        Static method because the worker only has object representations of tile data, there is no
        tile instance created yet.