Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.ServiceModel/System/ServiceModel/SessionMode.cs

@@ -0,0 +1,25 @@
+//-----------------------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+//-----------------------------------------------------------------------------
+
+namespace System.ServiceModel
+{
+    using System;
+
+    public enum SessionMode
+    {
+        Allowed,
+        Required,
+        NotAllowed,
+    }
+
+    static class SessionModeHelper
+    {
+        public static bool IsDefined(SessionMode sessionMode)
+        {
+            return (sessionMode == SessionMode.NotAllowed ||
+                    sessionMode == SessionMode.Allowed ||
+                    sessionMode == SessionMode.Required);
+        }
+    }
+}