src/vs/base/common/map.ts/LinkedMap/touch
class LinkedMap:	private touch(item: Item<K, V>, touch: Touch): void {
		if (!this._head || !this._tail) {
			throw new Error('Invalid list');
		}
		if ((touch !== Touch.AsOld && touch !== Touch.AsNew)) {
			return;
		}

		if (touch === Touch.AsOld) {
			if (item === this._head) {
				return;
			}

			const next = item.next;
			const previous = item.previous;

			// Unlink the item
			if (item === this._tail) {
				// previous must be defined since item was not head but is tail
				// So there are more than on item in the map
				previous!.next = undefined;
				this._tail = previous;
			}
			else {
				// Both next and previous are not undefined since item was neither head nor tail.
				next!.previous = previous;
				previous!.next = next;
			}

			// Insert the node at head
			item.previous = undefined;
			item.next = this._head;
			this._head.previous = item;
			this._head = item;
			this._state++;
		} else if (touch === Touch.AsNew) {
			if (item === this._tail) {
				return;
			}

			const next = item.next;
			const previous = item.previous;

			// Unlink the item.
			if (item === this._head) {
				// next must be defined since item was not tail but is head
				// So there are more than on item in the map
				next!.previous = undefined;
				this._head = next;
			} else {
				// Both next and previous are not undefined since item was neither head nor tail.
				next!.previous = previous;
				previous!.next = next;
			}
			item.next = undefined;
			item.previous = this._tail;
			this._tail.next = item;
			this._tail = item;
			this._state++;
		}
	}