src/vs/editor/common/viewLayout/viewLayout.ts/ViewLayout/getLinesViewportDataAtScrollTop
class ViewLayout:	public getLinesViewportDataAtScrollTop(scrollTop: number): IPartialViewLinesViewportData {
		// do some minimal validations on scrollTop
		const scrollDimensions = this._scrollable.getScrollDimensions();
		if (scrollTop + scrollDimensions.height > scrollDimensions.scrollHeight) {
			scrollTop = scrollDimensions.scrollHeight - scrollDimensions.height;
		}
		if (scrollTop < 0) {
			scrollTop = 0;
		}
		return this._linesLayout.getLinesViewportData(scrollTop, scrollTop + scrollDimensions.height);
	}