LinkedList = function () {

        /**
         * @type {module:zrender/core/LRU~Entry}
         */
        this.head = null;

        /**
         * @type {module:zrender/core/LRU~Entry}
         */
        this.tail = null;

        this._len = 0;
    }
Simple double linked list. Compared with array, it has O(1) remove operation.
@constructor