static shouldPreloadRequest(request, mainResource, initiatorPath) {
    // If it's already preloaded, no need to recommend it.
    if (request.isLinkPreload) return false;
    // It's not a request loaded over the network, don't recommend it.
    if (NetworkRequest.isNonNetworkRequest(request)) return false;
    // It's already discoverable from the main document (a path of [lcpRecord, mainResource]), don't recommend it.
    if (initiatorPath.length <= 2) return false;
    // Finally, return whether or not it belongs to the main frame
    return request.frameId === mainResource.frameId;
  }
@param {LH.Artifacts.NetworkRequest} request
@param {LH.Artifacts.NetworkRequest} mainResource
@param {InitiatorPath} initiatorPath
@return {boolean}