Comment registered key (#816)

src/Microsoft.AspNetCore.Routing/CompositeEndpointDataSource.cs

@@ -80,7 +80,7 @@ namespace Microsoft.AspNetCore.Routing
 
                     foreach (var dataSource in _dataSources)
                     {
-                        Extensions.Primitives.ChangeToken.OnChange(
+                        ChangeToken.OnChange(
                             dataSource.GetChangeToken,
                             HandleChange);
                     }

src/Microsoft.AspNetCore.Routing/Internal/EndpointRoutingApplicationBuilderExtensions.cs

@@ -11,6 +11,7 @@ namespace Microsoft.AspNetCore.Internal
 {
     public static class EndpointRoutingApplicationBuilderExtensions
     {
+        // Property key is used by MVC package to check that routing is registered
         private const string EndpointRoutingRegisteredKey = "__EndpointRoutingMiddlewareRegistered";
 
         public static IApplicationBuilder UseEndpointRouting(this IApplicationBuilder builder)

src/Microsoft.AspNetCore.Routing/RouteValuesBasedEndpointFinder.cs

@@ -8,6 +8,7 @@ using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Routing.Internal;
 using Microsoft.AspNetCore.Routing.Template;
 using Microsoft.AspNetCore.Routing.Tree;
+using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNetCore.Routing
 {
@@ -25,7 +26,7 @@ namespace Microsoft.AspNetCore.Routing
             BuildOutboundMatches();
 
             // Register for changes in endpoints
-            Extensions.Primitives.ChangeToken.OnChange(
+            ChangeToken.OnChange(
                 _dataSource.GetChangeToken,
                 HandleChange);
         }
@@ -61,7 +62,7 @@ namespace Microsoft.AspNetCore.Routing
 
             // re-register the callback as the change token is one time use only and a new change token
             // is produced every time
-            Extensions.Primitives.ChangeToken.OnChange(
+            ChangeToken.OnChange(
                 _dataSource.GetChangeToken,
                 HandleChange);
         }