FxCop for Preview handler (#6833)

src/modules/previewpane/UnitTests-PreviewHandlerCommon/NativeMethods.cs

@@ -0,0 +1,16 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Runtime.InteropServices;
+
+namespace PreviewHandlerCommonUnitTests
+{
+    public static class NativeMethods
+    {
+        // Gets the ancestor window: https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getancestor
+        [DllImport("user32.dll")]
+        internal static extern IntPtr GetAncestor(IntPtr hWnd, uint gaFlags);
+    }
+}