makeNetworkRequest_(request, type, context) {
    if (!context) {
      context = {};
    }
    context.isPreload = this.isPreloadFn_();
    const op = this.playerInterface_.networkingEngine.request(
        type, request, context);
    this.operationManager_.manage(op);
    return op.promise;
  }
Create a networking request. This will manage the request using the
parser's operation manager.

@param {shaka.extern.Request} request
@param {shaka.net.NetworkingEngine.RequestType} type
@param {shaka.extern.RequestContext=} context
@return {!Promise<shaka.extern.Response>}
@private