scrollbar PageUp/PageDown handling

src/Avalonia.Controls/Primitives/ScrollBar.cs

@@ -128,6 +128,20 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
+        protected override void OnKeyDown(KeyEventArgs e)
+        {
+            if (e.Key == Key.PageUp)
+            {
+                LargeDecrement();
+                e.Handled = true;
+            }
+            else if (e.Key == Key.PageDown)
+            {
+                LargeIncrement();
+                e.Handled = true;
+            }
+        }
+
         protected override void OnTemplateApplied(TemplateAppliedEventArgs e)
         {
             base.OnTemplateApplied(e);

src/Avalonia.Controls/ScrollViewer.cs

@@ -4,6 +4,7 @@
 using System;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
+using Avalonia.Input;
 
 namespace Avalonia.Controls
 {
@@ -441,5 +442,19 @@ namespace Avalonia.Controls
             RaisePropertyChanged(VerticalScrollBarValueProperty, 0, VerticalScrollBarValue);
             RaisePropertyChanged(VerticalScrollBarViewportSizeProperty, 0, VerticalScrollBarViewportSize);
         }
+
+        protected override void OnKeyDown(KeyEventArgs e)
+        {
+            if (e.Key == Key.PageUp)
+            {
+                VerticalScrollBarValue = Math.Max(_offset.Y - _viewport.Height, 0);
+                e.Handled = true;
+            }
+            else if (e.Key == Key.PageDown)
+            {
+                VerticalScrollBarValue = Math.Min(_offset.Y + _viewport.Height, VerticalScrollBarMaximum);
+                e.Handled = true;
+            }
+        }
     }
 }