Added failing Carousel leak test.

As found by @donandren.

tests/Perspex.LeakTests/ControlTests.cs

@@ -269,12 +269,12 @@ namespace Perspex.LeakTests
                     Content = target = new TreeView
                     {
                         DataTemplates = new DataTemplates
-                    {
-                        new FuncTreeDataTemplate<Node>(
-                            x => new TextBlock { Text = x.Name },
-                            x => x.Children,
-                            x => true)
-                    },
+                        {
+                            new FuncTreeDataTemplate<Node>(
+                                x => new TextBlock { Text = x.Name },
+                                x => x.Children,
+                                x => true)
+                        },
                         Items = nodes
                     }
                 };

tests/Perspex.LeakTests/StyleTests.cs

@@ -65,5 +65,64 @@ namespace Perspex.LeakTests
             dotMemory.Check(memory =>
                 Assert.Equal(0, memory.GetObjects(where => where.Type.Is<StyleActivator>()).ObjectsCount));
         }
+
+        [Fact]
+        public void Changing_Carousel_SelectedIndex_Should_Not_Leak_StyleActivators()
+        {
+            Func<Window> run = () =>
+            {
+                Carousel target;
+
+                var window = new Window
+                {
+                    Styles = new Styles
+                    {
+                        new Style(x => x.OfType<ContentControl>().Class("foo"))
+                        {
+                            Setters = new[]
+                            {
+                                new Setter(Visual.OpacityProperty, 0.5),
+                            }
+                        }
+                    },
+                    Content = target = new Carousel
+                    {
+                        Items = new[]
+                        {
+                            new ContentControl
+                            {
+                                Name = "item1",
+                                Classes = new Classes("foo"),
+                                Content = "item1",
+                            },
+                            new ContentControl
+                            {
+                                Name = "item2",
+                                Classes = new Classes("foo"),
+                                Content = "item2",
+                            },
+                        }
+                    }
+                };
+
+                // Do a layout and make sure that Carousel gets added to visual tree.
+                window.LayoutManager.ExecuteLayoutPass();
+                Assert.IsType<Carousel>(window.Presenter.Child);
+
+                target.SelectedIndex = 1;
+                window.LayoutManager.ExecuteLayoutPass();
+                target.SelectedIndex = 0;
+                window.LayoutManager.ExecuteLayoutPass();
+                target.SelectedIndex = 1;
+                window.LayoutManager.ExecuteLayoutPass();
+
+                return window;
+            };
+
+            var result = run();
+
+            dotMemory.Check(memory =>
+                Assert.Equal(1, memory.GetObjects(where => where.Type.Is<StyleActivator>()).ObjectsCount));
+        }
     }
 }