function cleanUpNextTick() {
	    if (!draining || !currentQueue) {
	        return;
	    }
	    draining = false;
	    if (currentQueue.length) {
	        queue = currentQueue.concat(queue);
	    } else {
	        queueIndex = -1;
	    }
	    if (queue.length) {
	        drainQueue();
	    }
	}
To reduce total package size of each coordinate systems, the modules `prepareCustom`
of each coordinate systems are not required by each coordinate systems directly, but
required by the module `custom`.

prepareInfoForCustomSeries {Function}: optional
    @return {Object} {coordSys: {...}, api: {
        coord: function (data, clamp) {}, // return point in global.
        size: function (dataSize, dataItem) {} // return size of each axis in coordSys.
    }}