static async getRawHsts(artifacts, context) {
    const devtoolsLog = artifacts.DevtoolsLog;
    const mainResource =
        await MainResource.request({devtoolsLog, URL: artifacts.URL}, context);

    let hstsHeaders =
        mainResource.responseHeaders
            .filter(h => {
              return h.name.toLowerCase() === 'strict-transport-security';
            })
            .flatMap(h => h.value.split(';'));

    // Sanitize the header value / directives.
    hstsHeaders = hstsHeaders.map(v => v.toLowerCase().replace(/\s/g, ''));

    return hstsHeaders;
  }
@param {LH.Artifacts} artifacts
@param {LH.Audit.Context} context
@return {Promise<string[]>}