async function getPreviousUrlMap(options) {
  const slug = getGitHubRepoSlug();
  if (!slug) return new Map();

  try {
    const fetchUrl = new URL(GET_URL_MAP_URL);
    fetchUrl.searchParams.set('slug', slug);
    const apiResponse = await fetch(fetchUrl.href);
    if (!apiResponse.ok) return new Map();
    const {success, url} = await apiResponse.json();
    if (!success) return new Map();
    const mapResponse = await fetch(url);
    if (mapResponse.status !== 200) return new Map();
    const entries = Object.entries(await mapResponse.json());
    return new Map(
      entries.map(([k, v]) => [replaceUrlPatterns(k, options.urlReplacementPatterns), v])
    );
  } catch (err) {
    print(`Error while fetching previous urlMap: ${err.message}`);
    return new Map();
  }
}
Fetches the last public URL mapping from master if it exists.

@param {LHCI.UploadCommand.Options} options
@return {Promise<Map<string, string>>}