src/vs/editor/common/viewLayout/viewLayout.ts/ViewLayout/getWhitespaceViewportData
class ViewLayout:	public getWhitespaceViewportData(): IViewWhitespaceViewportData[] {
		const visibleBox = this.getCurrentViewport();
		return this._linesLayout.getWhitespaceViewportData(visibleBox.top, visibleBox.top + visibleBox.height);
	}