Add Referer to GetTypedHeaders (#949)

* Add a Referer property

* Add Uri to KnownParsers

* Add property for Origin

* Add Origin

* Encode the URI

From feedback from Tratcher

* Inline the var 'out' declaration

* Remove Origin

Since it does not cleanly map to a Uri object since it can contain multiple values.

* Took back that whitespace

* Reverted

* Add using for UriHelper.Encode

src/Microsoft.AspNetCore.Http.Extensions/RequestHeaders.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using Microsoft.AspNetCore.Http.Extensions;
 using Microsoft.Net.Http.Headers;
 
 namespace Microsoft.AspNetCore.Http.Headers
@@ -261,6 +262,23 @@ namespace Microsoft.AspNetCore.Http.Headers
             }
         }
 
+        public Uri Referer
+        {
+            get
+            {
+                Uri uri;
+                if (Uri.TryCreate(Headers[HeaderNames.Referer], UriKind.RelativeOrAbsolute, out uri))
+                {
+                    return uri;
+                }
+                return null;
+            }
+            set
+            {
+                Headers.Set(HeaderNames.Referer, value == null ? null : UriHelper.Encode(value));
+            }
+        }
+
         public T Get<T>(string name)
         {
             return Headers.Get<T>(name);