honor UIA_WindowVisibilityOverridden property (#5839)

src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClient/MS/Internal/Automation/HwndProxyElementProvider.cs

@@ -574,7 +574,7 @@ WindowVisualState IWindowProvider.VisualState
 
         WindowInteractionState IWindowProvider.InteractionState
         {
-            // Note: we should consider Implementing InteractionState by finding the gui thread of the 
+            // Note: we should consider Implementing InteractionState by finding the gui thread of the
             // process and mapping ThreadState and WaitReason to a WindowInteractionState
             get
             {
@@ -1457,6 +1457,21 @@ private static bool IsWindowReallyEnabled( NativeMethods.HWND hwnd )
         // Check that a window is visible, and has a non-empty rect
         private static bool IsWindowReallyVisible( NativeMethods.HWND hwnd )
         {
+            // check for visibility overrides
+            // The UIA team says:
+            //      * UIA_WindowVisibilityOverridden property was added in 2011 for Win8.1
+            //      * "I'm not actually sure it is documented publicly."
+            //      * "It's a window property that if its handle value is 1 it's ForceVisible, and if it's 2 it's ForceHidden."
+            IntPtr visibilityOverride = UnsafeNativeMethods.GetProp(hwnd, "UIA_WindowVisibilityOverridden");
+            if (visibilityOverride == new IntPtr(1))
+            {
+                return true;
+            }
+            else if (visibilityOverride == new IntPtr(2))
+            {
+                return false;
+            }
+
             if(!SafeNativeMethods.IsWindowVisible(hwnd))
             {
                 return false;

src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClient/MS/Win32/UnsafeNativeMethods.cs

@@ -365,5 +365,12 @@ internal struct MENUBARINFO
         [DllImport("gdi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
         internal static extern bool DeleteObject(IntPtr hrgn);
 
+        //
+        // Window Property Functions
+        //
+
+        [DllImport("user32.dll", CharSet = CharSet.Unicode)]
+        internal static extern IntPtr GetProp(IntPtr hwnd, string name);
+
     }
 }