async getArtifact(passContext) {
    const driver = passContext.driver;

    const cacheUrls = await driver.executionContext.evaluate(getCacheContents, {args: []});
    return cacheUrls;
  }
Creates an array of cached URLs.
@param {LH.Gatherer.Context} passContext
@return {Promise<LH.Artifacts['CacheContents']>}