async getArtifact(context) {
    const devtoolsLog = context.dependencies.DevtoolsLog;
    const mainResource =
      await MainResource.request({devtoolsLog, URL: context.baseArtifacts.URL}, context);
    const session = context.driver.defaultSession;
    return fetchResponseBodyFromCache(session, mainResource.requestId);
  }
@param {LH.Gatherer.Context<'DevtoolsLog'>} context
@return {Promise<LH.Artifacts['MainDocumentContent']>}