src/vs/workbench/contrib/snippets/browser/snippetsService.ts/watch
function watch(service: IFileService, resource: URI, callback: () => any): IDisposable {
	return combinedDisposable(
		service.watch(resource),
		service.onDidFilesChange(e => {
			if (e.affects(resource)) {
				callback();
			}
		})
	);
}