src/vs/editor/contrib/folding/browser/foldingRanges.ts/FoldingRegions/findRange
class FoldingRegions:	public findRange(line: number): number {
		let index = this.findIndex(line);
		if (index >= 0) {
			let endLineNumber = this.getEndLineNumber(index);
			if (endLineNumber >= line) {
				return index;
			}
			index = this.getParentIndex(index);
			while (index !== -1) {
				if (this.contains(index, line)) {
					return index;
				}
				index = this.getParentIndex(index);
			}
		}
		return -1;
	}