_getEncodedResponse(session, requestId, encoding) {
    requestId = NetworkRequest.getRequestIdForBackend(requestId);

    const quality = encoding === 'jpeg' ? JPEG_QUALITY : WEBP_QUALITY;
    const params = {requestId, encoding, quality, sizeOnly: true};
    return session.sendCommand('Audits.getEncodedResponse', params);
  }
@param {LH.Gatherer.ProtocolSession} session
@param {string} requestId
@param {'jpeg'|'webp'} encoding Either webp or jpeg.
@return {Promise<LH.Crdp.Audits.GetEncodedResponseResponse>}