Imported Upstream version 3.6.0

Former-commit-id: da6be194a6b1221998fc28233f2503bd61dd9d14

external/aspnetwebstack/src/System.Web.Mvc/MvcHtmlString.cs

@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.
+
+using System.Diagnostics.CodeAnalysis;
+
+namespace System.Web.Mvc
+{
+    public sealed class MvcHtmlString : HtmlString
+    {
+        [SuppressMessage("Microsoft.Security", "CA2104:DoNotDeclareReadOnlyMutableReferenceTypes", Justification = "MvcHtmlString is immutable")]
+        public static readonly MvcHtmlString Empty = Create(String.Empty);
+
+        private readonly string _value;
+
+        public MvcHtmlString(string value)
+            : base(value ?? String.Empty)
+        {
+            _value = value ?? String.Empty;
+        }
+
+        public static MvcHtmlString Create(string value)
+        {
+            return new MvcHtmlString(value);
+        }
+
+        public static bool IsNullOrEmpty(MvcHtmlString value)
+        {
+            return (value == null || value._value.Length == 0);
+        }
+    }
+}