First programmatic smooth scroll should run on the compositor if it can

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 202 matching lines @@
     bool shouldSuspendScrollAnimations() const override;
     bool scrollbarsCanBeActive() const override;
     void scrollbarVisibilityChanged() override;
     IntRect scrollableAreaBoundingBox() const override;
     void registerForAnimation() override;
     void deregisterForAnimation() override;
     bool userInputScrollable(ScrollbarOrientation) const override;
     bool shouldPlaceVerticalScrollbarOnLeft() const override;
     int pageStep(ScrollbarOrientation) const override;
     ScrollBehavior scrollBehaviorStyle() const override;
+    CompositorAnimationTimeline* compositorAnimationTimeline() const override;
 
     double scrollXOffset() const { return m_scrollOffset.width() + scrollOrigin().x(); }
     double scrollYOffset() const { return m_scrollOffset.height() + scrollOrigin().y(); }
 
     DoubleSize scrollOffset() const { return m_scrollOffset; }
 
     // FIXME: We shouldn't allow access to m_overflowRect outside this class.
     LayoutRect overflowRect() const { return m_overflowRect; }
 
     void scrollToPosition(const DoublePoint& scrollPosition, ScrollOffsetClamping = ScrollOffsetUnclamped,
@@ skipping 193 matching lines @@
 #endif
 };
 
 DEFINE_TYPE_CASTS(PaintLayerScrollableArea, ScrollableArea, scrollableArea,
     scrollableArea->isPaintLayerScrollableArea(),
     scrollableArea.isPaintLayerScrollableArea());
 
 } // namespace blink
 
 #endif // LayerScrollableArea_h