AssetsWarmUpPolicy.cs

    public class AssetsWarmUpPolicy : IAssetPolicy
    {
        private readonly IAssetRequirements _requirements;
        private readonly IAssetTagPlanCache _planCache;
        public AssetsWarmUpPolicy(IAssetRequirements requirements, IAssetTagPlanCache planCache)
        {
            _requirements = requirements;
            _planCache = planCache;
        }

        public void Apply(IPackageLog log, IAssetPipeline pipeline, AssetGraph graph)
        {
            // WARM UP
            new[] { "site-css",..... }
                .Each(x =>
                {
                    _requirements.Require(x);
                    _requirements.DequeueAssetsToRender()
                        .Select(_planCache.PlanFor)
                        .ToList();
                });
        }
    }