src/vs/editor/contrib/folding/hiddenRangeModel.ts/HiddenRangeModel/constructor
class HiddenRangeModel:	public constructor(model: FoldingModel) {
		this._foldingModel = model;
		this._foldingModelListener = model.onDidChange(_ => this.updateHiddenRanges());
		this._hiddenRanges = [];
		if (model.regions.length) {
			this.updateHiddenRanges();
		}
	}