Make logical tree work for TabControl.

It only contains the currently visible tab - I'm not so happy about
this...

Perspex.Base/Collections/SingleItemPerspexList.cs

@@ -80,7 +80,7 @@ namespace Perspex.Collections
                 }
                 else
                 {
-                    e = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Replace, value, this.item);
+                    e = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Replace, value, this.item, 0);
                     this.item = value;
                 }
 

Perspex.Controls/Presenters/ContentPresenter.cs

@@ -32,7 +32,7 @@ namespace Perspex.Controls.Presenters
         {
             get
             {
-                return this.Child;
+                return this.child;
             }
 
             private set

Perspex.Controls/TabControl.cs

@@ -11,9 +11,10 @@ namespace Perspex.Controls
     using System.Reactive.Linq;
     using Perspex.Collections;
     using Perspex.Controls.Generators;
+    using Perspex.Controls.Presenters;
     using Perspex.Controls.Primitives;
 
-    public class TabControl : SelectingItemsControl
+    public class TabControl : SelectingItemsControl, ILogical
     {
         public static readonly PerspexProperty<object> SelectedContentProperty =
             PerspexProperty.Register<TabControl, object>("SelectedContent");
@@ -23,6 +24,12 @@ namespace Perspex.Controls
 
         private TabStrip tabStrip;
 
+        private ContentPresenter presenter;
+
+        private IDisposable presenterSubscription;
+
+        private SingleItemPerspexList<ILogical> logicalChild = new SingleItemPerspexList<ILogical>();
+
         public TabControl()
         {
             this.GetObservable(SelectedItemProperty).Subscribe(x =>
@@ -49,6 +56,11 @@ namespace Perspex.Controls
             private set { this.SetValue(SelectedTabProperty, value); }
         }
 
+        IReadOnlyPerspexList<ILogical> ILogical.LogicalChildren
+        {
+            get { return this.logicalChild; }
+        }
+
         protected override ItemContainerGenerator CreateItemContainerGenerator()
         {
             return new TypedItemContainerGenerator<TabItem>(this);
@@ -56,7 +68,20 @@ namespace Perspex.Controls
 
         protected override void OnTemplateApplied()
         {
-            base.OnTemplateApplied();
+            if (this.presenterSubscription != null)
+            {
+                this.presenterSubscription.Dispose();
+                this.presenterSubscription = null;
+            }
+
+            this.presenter = this.FindTemplateChild<ContentPresenter>("contentPresenter");
+
+            if (this.presenter != null)
+            {
+                this.presenterSubscription = this.presenter.ChildObservable
+                    .Subscribe(x => this.logicalChild.SingleItem = x);
+            }
+
             this.tabStrip = this.GetTemplateControls().OfType<TabStrip>().FirstOrDefault();
             this.BindTwoWay(TabControl.SelectedItemProperty, this.tabStrip, TabControl.SelectedItemProperty);
         }

Perspex.Themes.Default/TabItemStyle.cs

@@ -41,7 +41,7 @@ namespace Perspex.Themes.Default
         {
             return new ContentPresenter
             {
-                Id = "contentPresenter",
+                Id = "headerPresenter",
                 [~ContentPresenter.ContentProperty] = control[~TabItem.HeaderProperty],
             };
         }