Animations: Port ProgrammaticScrollAnimator to use compositor timelines

Source/platform/scroll/ScrollableArea.h

Index: Source/platform/scroll/ScrollableArea.h
diff --git a/Source/platform/scroll/ScrollableArea.h b/Source/platform/scroll/ScrollableArea.h
index e1f8d3d2c7a3dc5c9f5b30fbff99b660edf42335..92b9af70d50ac2f750138633a5be3b58d4981ed4 100644
--- a/Source/platform/scroll/ScrollableArea.h
+++ b/Source/platform/scroll/ScrollableArea.h
@@ -46,6 +46,7 @@ class PlatformWheelEvent;
 class ProgrammaticScrollAnimator;
 struct ScrollAlignment;
 class ScrollAnimator;
+class WebCompositorAnimationTimeline;
 
 enum ScrollBehavior {
     ScrollBehaviorAuto,
@@ -268,7 +269,7 @@ public:
     bool hasLayerForVerticalScrollbar() const;
     bool hasLayerForScrollCorner() const;
 
-    void layerForScrollingDidChange();
+    void layerForScrollingDidChange(WebCompositorAnimationTimeline*);
 
     void cancelScrollAnimation();
     void cancelProgrammaticScrollAnimation();