async fetchSourceMap(driver, sourceMapUrl) {
    const response = await driver.fetcher.fetchResource(sourceMapUrl, {timeout: 1500});
    if (response.content === null) {
      throw new Error(`Failed fetching source map (${response.status})`);
    }
    return SDK.SourceMap.parseSourceMap(response.content);
  }
@param {LH.Gatherer.Driver} driver
@param {string} sourceMapUrl
@return {Promise<LH.Artifacts.RawSourceMap>}