Added failing test for #1065.

Also add setter for `ScrollContentPresenter.CanScrollHorizontally`.

src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs

@@ -101,9 +101,13 @@ namespace Avalonia.Controls.Presenters
         }
 
         /// <summary>
-        /// Gets a value indicating whether the content can be scrolled horizontally.
+        /// Gets or sets a value indicating whether the content can be scrolled horizontally.
         /// </summary>
-        public bool CanScrollHorizontally => GetValue(CanScrollHorizontallyProperty);
+        public bool CanScrollHorizontally
+        {
+            get => GetValue(CanScrollHorizontallyProperty);
+            set => SetValue(CanScrollHorizontallyProperty, value);
+        }
 
         /// <summary>
         /// Attempts to bring a portion of the target visual into view by scrolling the content.
@@ -213,8 +217,8 @@ namespace Avalonia.Controls.Presenters
                 if (child != null)
                 {
                     var size = new Size(
-                    Math.Max(finalSize.Width, child.DesiredSize.Width),
-                    Math.Max(finalSize.Height, child.DesiredSize.Height));
+                        Math.Max(finalSize.Width, child.DesiredSize.Width),
+                        Math.Max(finalSize.Height, child.DesiredSize.Height));
                     child.Arrange(new Rect((Point)(-Offset), size));
                     return finalSize;
                 }

tests/Avalonia.Controls.UnitTests/Presenters/ScrollContentPresenterTests.cs

@@ -201,6 +201,32 @@ namespace Avalonia.Controls.UnitTests.Presenters
             Assert.Equal(new[] { "Viewport", "Extent" }, set);
         }
 
+        [Fact]
+        public void Arrange_Should_Constrain_Child_Width_When_CanScrollHorizontally_False()
+        {
+            var child = new WrapPanel
+            {
+                Children =
+                {
+                    new Border { Width = 40, Height = 50 },
+                    new Border { Width = 40, Height = 50 },
+                    new Border { Width = 40, Height = 50 },
+                }
+            };
+
+            var target = new ScrollContentPresenter
+            {
+                Content = child,
+                CanScrollHorizontally = false,
+            };
+
+            target.UpdateChild();
+            target.Measure(Size.Infinity);
+            target.Arrange(new Rect(0, 0, 100, 100));
+
+            Assert.Equal(100, child.Bounds.Width);
+        }
+
         [Fact]
         public void Setting_Offset_Should_Invalidate_Arrange()
         {