onLinesDeleted(fromLineNumber, toLineNumber) {
        this._checkPendingChanges();
        fromLineNumber = fromLineNumber | 0;
        toLineNumber = toLineNumber | 0;
        this._lineCount -= (toLineNumber - fromLineNumber + 1);
        for (let i = 0, len = this._arr.length; i < len; i++) {
            const afterLineNumber = this._arr[i].afterLineNumber;
            if (fromLineNumber <= afterLineNumber && afterLineNumber <= toLineNumber) {
                // The line this whitespace was after has been deleted
                //  => move whitespace to before first deleted line
                this._arr[i].afterLineNumber = fromLineNumber - 1;
            }
            else if (afterLineNumber > toLineNumber) {
                // The line this whitespace was after has been moved up
                //  => move whitespace up
                this._arr[i].afterLineNumber -= (toLineNumber - fromLineNumber + 1);
            }
        }
    }
Notify the layouter that lines have been deleted (a continuous zone of lines).

@param fromLineNumber The line number at which the deletion started, inclusive
@param toLineNumber The line number at which the deletion ended, inclusive