No longer set first window opened as MainWindow

samples/ControlCatalog/App.xaml.cs

@@ -15,6 +15,8 @@ namespace ControlCatalog
             var mainWindow = new MainWindow();
 
             mainWindow.Show();
+
+            MainWindow = mainWindow;
         }
     }
 }

src/Avalonia.Controls/Application.cs

@@ -272,6 +272,8 @@ namespace Avalonia
                 {
                     mainWindow.Show();
                 }
+
+                MainWindow = mainWindow;
             }
 
             Run(_mainLoopCancellationTokenSource.Token);

src/Avalonia.Controls/Window.cs

@@ -49,8 +49,6 @@ namespace Avalonia.Controls
     /// </summary>
     public class Window : WindowBase, IStyleable, IFocusScope, ILayoutRoot, INameScope
     {
-        private static bool s_hasAddedFirstWindow;
-
         /// <summary>
         /// Defines the <see cref="SizeToContent"/> property.
         /// </summary>
@@ -262,18 +260,6 @@ namespace Avalonia.Controls
             }
 
             Application.Current.Windows.Add(window);
-
-            if (s_hasAddedFirstWindow)
-            {
-                return;
-            }
-
-            s_hasAddedFirstWindow = true;
-
-            if (Application.Current.MainWindow == null)
-            {
-                Application.Current.MainWindow = window;
-            }
         }
 
         private static void RemoveWindow(Window window)

tests/Avalonia.Controls.UnitTests/ApplicationTests.cs

@@ -129,18 +129,5 @@ namespace Avalonia.Controls.UnitTests
                 Assert.True(raised);
             }
         }
-
-        [Fact]
-        public void Should_Have_MainWindow_After_First_Window_Shown()
-        {
-            using (UnitTestApplication.Start(TestServices.StyledWindow))
-            {                
-                var mainWindow = new Window();
-
-                mainWindow.Show();            
-
-                Assert.Equal(mainWindow, Application.Current.MainWindow);
-            }
-        }
     }
 }