Fix frame end task race condition in ScrollPanelWidget

OpenRA.Game/Primitives/ObservableCollection.cs

@@ -18,15 +18,15 @@ namespace OpenRA.Primitives
 {
 	public class ObservableCollection<T> : Collection<T>, IObservableCollection
 	{
-		public event Action<object> OnAdd = k => { };
+		public event Action<IObservableCollection, object> OnAdd = (x, k) => { };
 
 		// TODO Workaround for https://github.com/OpenRA/OpenRA/issues/6101
 		#pragma warning disable 67
-		public event Action<object> OnRemove = k => { };
+		public event Action<IObservableCollection, object> OnRemove = (x, k) => { };
 		#pragma warning restore
-		public event Action<int> OnRemoveAt = i => { };
-		public event Action<object, object> OnSet = (o, n) => { };
-		public event Action OnRefresh = () => { };
+		public event Action<IObservableCollection, int> OnRemoveAt = (x, i) => { };
+		public event Action<IObservableCollection, object, object> OnSet = (x, o, n) => { };
+		public event Action<IObservableCollection> OnRefresh = x => { };
 
 		public ObservableCollection() { }
 		public ObservableCollection(IList<T> list) : base(list) { }
@@ -35,25 +35,25 @@ namespace OpenRA.Primitives
 		{
 			var old = this[index];
 			base.SetItem(index, item);
-			OnSet(old, item);
+			OnSet(this, old, item);
 		}
 
 		protected override void InsertItem(int index, T item)
 		{
 			base.InsertItem(index, item);
-			OnAdd(item);
+			OnAdd(this, item);
 		}
 
 		protected override void ClearItems()
 		{
 			base.ClearItems();
-			OnRefresh();
+			OnRefresh(this);
 		}
 
 		protected override void RemoveItem(int index)
 		{
 			base.RemoveItem(index);
-			OnRemoveAt(index);
+			OnRemoveAt(this, index);
 		}
 
 		public IEnumerable ObservedItems