Make Window and Popup respect layout properties.

Had to remove syncing client size to `Width`/`Height` in `PopupRoot` bceause without the `SizeToContent` property it was impossible to tell whether its `Width`/`Height` came from a requested bound or from the actual window size.

src/Avalonia.Controls/Primitives/PopupRoot.cs

@@ -117,6 +117,33 @@ namespace Avalonia.Controls.Primitives
             });
         }
 
+        protected override Size MeasureOverride(Size availableSize)
+        {
+            var measured = base.MeasureOverride(availableSize);
+            var width = measured.Width;
+            var height = measured.Height;
+            var widthCache = Width;
+            var heightCache = Height;
+
+            if (!double.IsNaN(widthCache))
+            {
+                width = widthCache;
+            }
+
+            width = Math.Min(width, MaxWidth);
+            width = Math.Max(width, MinWidth);
+
+            if (!double.IsNaN(heightCache))
+            {
+                height = heightCache;
+            }
+
+            height = Math.Min(height, MaxHeight);
+            height = Math.Max(height, MinHeight);
+
+            return new Size(width, height);
+        }
+
         protected override sealed Size ArrangeSetBounds(Size size)
         {
             using (BeginAutoSizing())

src/Avalonia.Controls/Window.cs

@@ -570,8 +570,8 @@ namespace Avalonia.Controls
         protected override Size MeasureOverride(Size availableSize)
         {
             var sizeToContent = SizeToContent;
+            var constraint = availableSize;
             var clientSize = ClientSize;
-            var constraint = clientSize;
 
             if (sizeToContent.HasFlagCustom(SizeToContent.Width))
             {
@@ -587,12 +587,26 @@ namespace Avalonia.Controls
 
             if (!sizeToContent.HasFlagCustom(SizeToContent.Width))
             {
-                result = result.WithWidth(clientSize.Width);
+                if (!double.IsInfinity(availableSize.Width))
+                {
+                    result = result.WithWidth(availableSize.Width);
+                }
+                else
+                {
+                    result = result.WithWidth(clientSize.Width);
+                }
             }
 
             if (!sizeToContent.HasFlagCustom(SizeToContent.Height))
             {
-                result = result.WithHeight(clientSize.Height);
+                if (!double.IsInfinity(availableSize.Height))
+                {
+                    result = result.WithHeight(availableSize.Height);
+                }
+                else
+                {
+                    result = result.WithHeight(clientSize.Height);
+                }
             }
 
             return result;
@@ -622,6 +636,9 @@ namespace Avalonia.Controls
                 SizeToContent = SizeToContent.Manual;
             }
 
+            Width = clientSize.Width;
+            Height = clientSize.Height;
+
             base.HandleResized(clientSize);
         }
 

src/Avalonia.Controls/WindowBase.cs

@@ -224,8 +224,6 @@ namespace Avalonia.Controls
         /// <param name="clientSize">The new client size.</param>
         protected override void HandleResized(Size clientSize)
         {
-            Width = clientSize.Width;
-            Height = clientSize.Height;
             ClientSize = clientSize;
             LayoutManager.ExecuteLayoutPass();
             Renderer?.Resized(clientSize);