Use Json result constructor only from the Action result helper.

Names to be changed, as they don't make much sense at the moment. Keeping them the same for diffing purposes

samples/MvcSample/Home2Controller.cs

@@ -42,15 +42,7 @@ namespace MvcSample
 
         public IActionResult UserJson()
         {
-            return new JsonResult(_user)
-            {
-                Encoding = Encoding.UTF8
-            };
-        }
-
-        public IActionResult HelperUserJson()
-        {
-            JsonResult jsonResult = (JsonResult)Result.Json(_user);
+            var jsonResult = Result.Json(_user);
             jsonResult.Indent = false;
 
             return jsonResult;

src/Microsoft.AspNet.Mvc/ActionResultFactory.cs

@@ -4,6 +4,13 @@ namespace Microsoft.AspNet.Mvc
 {
     public class ActionResultFactory : IActionResultFactory
     {
+        private readonly IActionResultHelper _result;
+
+        public ActionResultFactory(IActionResultHelper result)
+        {
+            _result = result;
+        }
+
         public IActionResult CreateActionResult(Type declaredReturnType, object actionReturnValue, RequestContext requestContext)
         {
             // optimize common path
@@ -45,7 +52,7 @@ namespace Microsoft.AspNet.Mvc
                 };
             }
 
-            return new JsonResult(actionReturnValue);
+            return _result.Json(actionReturnValue);
         }
     }
 }

src/Microsoft.AspNet.Mvc/ActionResultHelper.cs

@@ -30,7 +30,7 @@ namespace Microsoft.AspNet.Mvc
             };
         }
 
-        public IActionResult Json(object value)
+        public IJsonResult Json(object value)
         {
             return new JsonResult(value);
         }

src/Microsoft.AspNet.Mvc/ActionResults/IJsonResult.cs

@@ -0,0 +1,10 @@
+using System.Text;
+
+namespace Microsoft.AspNet.Mvc
+{
+    public interface IJsonResult : IActionResult
+    {
+        Encoding Encoding { get; set; }
+        bool Indent { get; set; }
+    }
+}

src/Microsoft.AspNet.Mvc/ActionResults/JsonResult.cs

@@ -7,7 +7,7 @@ using Newtonsoft.Json;
 
 namespace Microsoft.AspNet.Mvc
 {
-    public class JsonResult : IActionResult
+    public class JsonResult : IJsonResult
     {
         private readonly object _returnValue;
 

src/Microsoft.AspNet.Mvc/IActionResultHelper.cs

@@ -5,7 +5,7 @@ namespace Microsoft.AspNet.Mvc
     {
         IActionResult Content(string value);
         IActionResult Content(string value, string contentType);
-        IActionResult Json(object value);
+        IJsonResult Json(object value);
         IActionResult View(string view, ViewData viewData);
     }
 }