Vsp freeze

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Primitives/HierarchicalVirtualizationConstraints.cs

@@ -21,6 +21,7 @@ public HierarchicalVirtualizationConstraints(VirtualizationCacheLength cacheLeng
  _cacheLength = cacheLength;
  _cacheLengthUnit = cacheLengthUnit;
  _viewport = viewport;
+ _scrollGeneration = 0; // internal field set separately by caller
  }
 
  #endregion
@@ -131,11 +132,22 @@ public override int GetHashCode()
 
  #endregion
 
+ #region Internal properties
+
+ internal long ScrollGeneration
+ {
+ get { return _scrollGeneration; }
+ set { _scrollGeneration = value; }
+ }
+
+ #endregion
+
  #region Data
 
  VirtualizationCacheLength _cacheLength;
  VirtualizationCacheLengthUnit _cacheLengthUnit;
  Rect _viewport;
+ long _scrollGeneration;
 
  #endregion
  }