Make sure extension window closes with Dynamo (#10557)

View extensions that add a Window to the extension bar, run the risk of
leaving a window open when Dynamo closes, resulting in a zombie process
. The extension could avoid the problem in either of these two ways:

1. Setting the Owner property of the Window they create to the one
obtained from ViewLoadedParam.DynamoWindow.

2. Calling the Close method on the Window they created when the
Shutdown life-time method is called on the extension.

However, Dynamo should not rely on view extensions doing this. In order
to be able to still close no matter what, we assign the Owner property
explicitly in DynamoView.AddExtensionTabItem.

src/DynamoCoreWpf/Views/Core/DynamoView.xaml.cs

@@ -230,6 +230,12 @@ internal TabItem AddExtensionTabItem(IViewExtension viewExtension, ContentContro
                 else
                 {
                     tab.Content = contentControl.Content;
+                    var extensionWindow = contentControl as Window;
+                    if (extensionWindow != null)
+                    {
+                        // Make sure the extension window closes with Dynamo
+                        extensionWindow.Owner = this;
+                    }
                 }
 
                 //Insert the tab at the end

test/DynamoCoreWpfTests/ViewExtensions/ViewExtensionTests.cs

@@ -26,6 +26,23 @@ public void OnWorkspaceChangedExtensionIsNotified()
             Assert.AreEqual(2, viewExtension.Counter);
         }
 
+        [Test]
+        public void ExtensionWindowIsClosedWithDynamo()
+        {
+            var dummyExtension = new DummyViewExtension()
+            {
+                SetOwner = false
+            };
+
+            RaiseLoadedEvent(this.View);
+            var extensionManager = View.viewExtensionManager;
+            extensionManager.Add(dummyExtension);
+
+            View.Close();
+
+            Assert.IsTrue(dummyExtension.WindowClosed);
+        }
+
         [Test]
         public void ExtensionsSideBarExtensionsTest()
         {
@@ -63,7 +80,9 @@ public static void RaiseLoadedEvent(FrameworkElement element)
 
     public class DummyViewExtension : IViewExtension
     {
-        public int Counter = 0;
+        public int Counter { get; set; }
+        public bool SetOwner { get; set; } = true;
+        public bool WindowClosed { get; set; }
 
         public string UniqueId
         {
@@ -87,11 +106,15 @@ public void Loaded(ViewLoadedParams p)
                 Counter++;
             };
 
-            var window = new Window
+            var window = new Window();
+            window.Closed += (sender, args) =>
             {
-                // Set the owner of the window to tuIDhe Dynamo window.
-                Owner = p.DynamoWindow
+                WindowClosed = true;
             };
+            if (SetOwner)
+            {
+                window.Owner = p.DynamoWindow;
+            }
 
             p.AddToExtensionsSideBar(this, window);
         }
@@ -138,7 +161,6 @@ public void Loaded(ViewLoadedParams p)
 
             var window = new Window
             {
-                // Set the owner of the window to tuIDhe Dynamo window.
                 Owner = p.DynamoWindow
             };