What calls RouteProvider.RegisterRoutes() Method

I see RouteProvider.cs class in each Plugin, etc. but I wonder what calls these methods and where? It is a partial class but since they have their own namespaces, they cannot be combined. What class registers all these providers to RouteTable?

public partial class RouteProvider : IRouteProvider
    {
        public void RegisterRoutes(RouteCollection routes)
        {
            routes.MapRoute("Plugin.Widgets.GoogleAnalytics.Configure",
                 "Plugins/WidgetsGoogleAnalytics/Configure",
                 new { controller = "WidgetsGoogleAnalytics", action = "Configure" },
                 new[] { "Nop.Plugin.Widgets.GoogleAnalytics.Controllers" }
            );

            //routes.MapRoute("Plugin.Widgets.GoogleAnalytics.PublicInfo",
            //     "Plugins/WidgetsGoogleAnalytics/PublicInfo",
            //     new { controller = "WidgetsGoogleAnalytics", action = "PublicInfo" },
            //     new[] { "Nop.Plugin.Widgets.GoogleAnalytics.Controllers" }
            //);
        }
        public int Priority
        {
            get
            {
                return 0;
            }
        }
    }

RoutePublisher in Nop.Web.Framework.Mvc.Routes

Thanks for the response but what calls RegisterRoutes() method in Nop.Web.Framework.Mvc.Routes.RoutePublisher. It seems something instantiate this class and pass a TypeFinder object which finds all the IRouteProvider. But I like to lean to see how this TypeFinder is implemented and what instantiates this RoutePublisher.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Routing;
using Nop.Core.Infrastructure;

namespace Nop.Web.Framework.Mvc.Routes
{
    public class RoutePublisher : IRoutePublisher
    {
        private readonly ITypeFinder _typeFinder;

        public RoutePublisher(ITypeFinder typeFinder)
        {
            this._typeFinder = typeFinder;
        }

        public void RegisterRoutes(RouteCollection routes)
        {
            var routeProviderTypes = _typeFinder.FindClassesOfType<IRouteProvider>();
            var routeProviders = new List<IRouteProvider>();
            foreach (var providerType in routeProviderTypes)
            {
                var provider = Activator.CreateInstance(providerType) as IRouteProvider;
                routeProviders.Add(provider);
            }
            routeProviders = routeProviders.OrderByDescending(rp => rp.Priority).ToList();
            routeProviders.ForEach(rp => rp.RegisterRoutes(routes));
        }
    }
}

In global.asax.cs IRoutePublisher is resolved to RoutePublisher (as defined in DependencyRegistrar)
and method RegisterRoutes is called.

RegisterRoutes uses ITypeFinder to load all assemblies and look for a specific type (IRouteProvider
in this case).

ITypeFinder is implemented by AppDomainTypeFinder and inherited by WebAppTypeFinder.
WebAppTypeFinder is setup to resolve ITypeFinder, this happens in ContainerConfigurer.

To Summarize: On startup RoutePublisher.RegisterRoutes is called, which in turn uses AppDomainTypeFinder  via WebAppTypeFinder to load all instances of IRouteProvider and call its RegisterRoutes method.