src/vs/workbench/contrib/terminal/browser/addons/commandTrackerAddon.ts/CommandTrackerAddon/_addMarkerOrThrow
class CommandTrackerAddon:	private _addMarkerOrThrow(xterm: Terminal, cursorYOffset: number): IMarker {
		const marker = xterm.addMarker(cursorYOffset);
		if (!marker) {
			throw new Error(`Could not create marker for ${cursorYOffset}`);
		}
		return marker;
	}