test: Additional launch assertions for ContentIsland

src/SamplesApp/SamplesApp.Shared/MainPage.xaml.cs

@@ -2,6 +2,7 @@
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Navigation;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 
 namespace SamplesApp
 {

src/SamplesApp/SamplesApp.UnitTests.Shared/Controls/UITests/Views/Controls/SampleChooserControl.xaml.cs

@@ -62,6 +62,12 @@ private void OnXamlRootChanged(XamlRoot sender, XamlRootChangedEventArgs args)
 
 		protected override Size MeasureOverride(Size availableSize)
 		{
+			Assert.IsTrue(IsLoaded, "The control should be loaded before the first measure.");
+			Assert.IsNotNull(XamlRoot, "Child should not be null.");
+#if HAS_UNO
+			Assert.IsNotNull(XamlRoot?.VisualTree.ContentRoot.CompositionContent, "ContentIsland of the ContentRoot should have been set by now.");
+#endif
+
 			if (_initialMeasure && availableSize == default)
 			{
 				_initialMeasure = false;

src/Uno.UI.Runtime.Skia.Wpf/Extensions/WpfDisplayInformationExtension.cs

@@ -2,10 +2,10 @@
 using System;
 using System.Windows;
 using System.Windows.Media;
-using Windows.ApplicationModel.Core;
-using Windows.Graphics.Display;
 using Microsoft.UI.Windowing;
 using Uno.UI.Runtime.Skia.Wpf.UI.Controls;
+using Windows.ApplicationModel.Core;
+using Windows.Graphics.Display;
 using WpfApplication = global::System.Windows.Application;
 using WpfWindow = global::System.Windows.Window;
 
@@ -41,7 +41,7 @@ private WpfWindow GetWindow()
 				// TODO: this is a ridiculous amount of indirection, find something better
 				if (!AppWindow.TryGetFromWindowId(_displayInformation.WindowId, out var appWindow) ||
 					Microsoft.UI.Xaml.Window.GetFromAppWindow(appWindow) is not { } window ||
-					UnoWpfWindow.GetWpfWindowFromWindow(window) is not { } wpfWindow)
+					UnoWpfWindow.GetFromWinUIWindow(window) is not { } wpfWindow)
 				{
 					throw new InvalidOperationException($"{nameof(WpfDisplayInformationExtension)} couldn't find a WPF window.");
 				}

src/Uno.UI.XamlHost.Skia.Wpf/UnoXamlHostBase.host.cs

@@ -10,6 +10,7 @@
 using Uno.UI.Runtime.Skia.Wpf.Extensions;
 using Uno.UI.Hosting;
 using Uno.UI.Runtime.Skia.Wpf;
+using Microsoft.UI.Content;
 
 namespace Uno.UI.XamlHost.Skia.Wpf;
 

src/Uno.UI/UI/Content/IContentIslandHost.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Uno.UI.Content;
+
+/// <summary>
+/// Represents a hosting site for a ContentIsland.
+/// </summary>
+internal interface IContentIslandHost
+{
+	float RasterizationScale { get; }
+
+	bool IsSiteVisible { get; }
+}