ZoneDelegate.prototype._updateTaskCount = function (type, count) {
                var counts = this._taskCounts;
                var prev = counts[type];
                var next = counts[type] = prev + count;
                if (next < 0) {
                    throw new Error('More tasks executed then were scheduled.');
                }
                if (prev == 0 || next == 0) {
                    var isEmpty = {
                        microTask: counts.microTask > 0,
                        macroTask: counts.macroTask > 0,
                        eventTask: counts.eventTask > 0,
                        change: type
                    };
                    try {
                        this.hasTask(this.zone, isEmpty);
                    }
                    finally {
                        if (this._parentDelegate) {
                            this._parentDelegate._updateTaskCount(type, count);
                        }
                    }
                }
            };