Use TaskCache class from Microsoft.Extensions.TaskCache.Sources (#331)

Instead of Task.FromResult(0)

src/Microsoft.AspNetCore.Diagnostics/ExceptionHandler/ExceptionHandlerMiddleware.cs

@@ -6,6 +6,7 @@ using System.Diagnostics;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Internal;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using Microsoft.Net.Http.Headers;
@@ -99,7 +100,7 @@ namespace Microsoft.AspNetCore.Diagnostics
             response.Headers[HeaderNames.Pragma] = "no-cache";
             response.Headers[HeaderNames.Expires] = "-1";
             response.Headers.Remove(HeaderNames.ETag);
-            return Task.FromResult(0);
+            return TaskCache.CompletedTask;
         }
     }
 }

src/Microsoft.AspNetCore.Diagnostics/StatusCodePage/StatusCodePagesExtensions.cs

@@ -6,6 +6,7 @@ using System.Globalization;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Diagnostics;
 using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Internal;
 using Microsoft.Extensions.Options;
 
 namespace Microsoft.AspNetCore.Builder
@@ -118,7 +119,7 @@ namespace Microsoft.AspNetCore.Builder
                 {
                     var location = string.Format(CultureInfo.InvariantCulture, locationFormat, context.HttpContext.Response.StatusCode);
                     context.HttpContext.Response.Redirect(context.HttpContext.Request.PathBase + location);
-                    return Task.FromResult(0);
+                    return TaskCache.CompletedTask;
                 });
             }
             else
@@ -127,7 +128,7 @@ namespace Microsoft.AspNetCore.Builder
                 {
                     var location = string.Format(CultureInfo.InvariantCulture, locationFormat, context.HttpContext.Response.StatusCode);
                     context.HttpContext.Response.Redirect(location);
-                    return Task.FromResult(0);
+                    return TaskCache.CompletedTask;
                 });
             }
         }

src/Microsoft.AspNetCore.Diagnostics/project.json

@@ -39,6 +39,10 @@
       "type": "build",
       "version": "1.1.0-*"
     },
+    "Microsoft.Extensions.TaskCache.Sources": {
+      "version": "1.1.0-*",
+      "type": "build"
+    },
     "Microsoft.Extensions.TypeNameHelper.Sources": {
       "type": "build",
       "version": "1.1.0-*"