Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Configuration/System/Configuration/EmptyImpersonationContext.cs

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+//------------------------------------------------------------------------------
+// <copyright file="EmptyImpersonationContext.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+namespace System.Configuration {
+    using System.Configuration.Internal;
+    using System.Collections;
+    using System.Collections.Specialized;
+    using System.Configuration;
+    using System.Globalization;
+    using System.IO;
+    using System.Runtime.InteropServices;
+    using System.Security.Permissions;
+    using System.Security;
+    using System.Text;
+    using System.Xml;
+
+    // An impersonation context that does nothing
+    // Used in cases where the Host does not require impersonation.
+    class EmptyImpersonationContext : IDisposable {
+        static volatile IDisposable s_emptyImpersonationContext;
+
+        static internal IDisposable GetStaticInstance() {
+            if (s_emptyImpersonationContext == null) {
+                s_emptyImpersonationContext = new EmptyImpersonationContext();
+            }
+
+            return s_emptyImpersonationContext;
+        }
+
+        public void Dispose() {}
+    }
+}