src/vs/editor/browser/viewParts/lines/viewLines.ts/ViewLines/_getLineNumberFor
class ViewLines:	private _getLineNumberFor(domNode: HTMLElement): number {
		const startLineNumber = this._visibleLines.getStartLineNumber();
		const endLineNumber = this._visibleLines.getEndLineNumber();
		for (let lineNumber = startLineNumber; lineNumber <= endLineNumber; lineNumber++) {
			const line = this._visibleLines.getVisibleLine(lineNumber);
			if (domNode === line.getDomNode()) {
				return lineNumber;
			}
		}
		return -1;
	}