An `ObjectPoolProvider` is always registered

- react to aspnet/Hosting/pull#673

src/Microsoft.AspNetCore.Routing/DependencyInjection/RoutingServiceCollectionExtensions.cs

@@ -28,7 +28,6 @@ namespace Microsoft.Extensions.DependencyInjection
 
             services.TryAddTransient<IInlineConstraintResolver, DefaultInlineConstraintResolver>();
             services.TryAddSingleton(UrlEncoder.Default);
-            services.TryAddSingleton<ObjectPoolProvider>(new DefaultObjectPoolProvider());
             services.TryAddSingleton<ObjectPool<UriBuildingContext>>(s =>
             {
                 var provider = s.GetRequiredService<ObjectPoolProvider>();

test/Microsoft.AspNetCore.Routing.Tests/RequestDelegateRouteBuilderExtensionsTest.cs

@@ -7,7 +7,7 @@ using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Internal;
 using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.ObjectPool;
 using Moq;
 using Xunit;
 
@@ -128,6 +128,7 @@ namespace Microsoft.AspNetCore.Routing
         private static IServiceProvider CreateServices()
         {
             var services = new ServiceCollection();
+            services.AddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
             services.AddOptions();
             services.AddRouting();
             services.AddLogging();

test/Microsoft.AspNetCore.Routing.Tests/RouteCollectionTest.cs

@@ -10,6 +10,7 @@ using Microsoft.AspNetCore.Http.Internal;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Testing;
+using Microsoft.Extensions.ObjectPool;
 using Microsoft.Extensions.Options;
 using Moq;
 using Xunit;
@@ -528,6 +529,7 @@ namespace Microsoft.AspNetCore.Routing
             var request = new Mock<HttpRequest>(MockBehavior.Strict);
 
             var services = new ServiceCollection();
+            services.AddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
             services.AddOptions();
             services.AddRouting();
             if (options != null)
@@ -549,6 +551,7 @@ namespace Microsoft.AspNetCore.Routing
         {
             var services = new ServiceCollection();
             services.AddSingleton<ILoggerFactory>(NullLoggerFactory.Instance);
+            services.AddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
             services.AddOptions();
             services.AddRouting();
             if (options != null)

test/Microsoft.AspNetCore.Routing.Tests/RouteTest.cs

@@ -14,6 +14,7 @@ using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Testing;
+using Microsoft.Extensions.ObjectPool;
 using Moq;
 using Xunit;
 
@@ -1383,6 +1384,7 @@ namespace Microsoft.AspNetCore.Routing
         {
             var services = new ServiceCollection();
             services.AddSingleton<ILoggerFactory>(NullLoggerFactory.Instance);
+            services.AddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
             services.AddRouting();
 
             var context = new DefaultHttpContext