Implement CSSOM smooth scroll for Elements

Source/core/rendering/RenderLayerScrollableArea.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 91 matching lines @@
     virtual IntPoint maximumScrollPosition() const override;
     virtual IntRect visibleContentRect(IncludeScrollbarsInRect) const override;
     virtual int visibleHeight() const override;
     virtual int visibleWidth() const override;
     virtual IntSize contentsSize() const override;
     virtual IntSize overhangAmount() const override;
     virtual IntPoint lastKnownMousePosition() const override;
     virtual bool shouldSuspendScrollAnimations() const override;
     virtual bool scrollbarsCanBeActive() const override;
     virtual IntRect scrollableAreaBoundingBox() const override;
+    virtual void registerForAnimation() override;
+    virtual void deregisterForAnimation() override;
     virtual bool userInputScrollable(ScrollbarOrientation) const override;
     virtual bool shouldPlaceVerticalScrollbarOnLeft() const override;
     virtual int pageStep(ScrollbarOrientation) 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 scrollToOffset(const DoubleSize& scrollOffset, ScrollOffsetClamping = ScrollOffsetUnclamped);
-    void scrollToXOffset(double x, ScrollOffsetClamping clamp = ScrollOffsetUnclamped) { scrollToOffset(DoubleSize(x, scrollYOffset()), clamp); }
-    void scrollToYOffset(double y, ScrollOffsetClamping clamp = ScrollOffsetUnclamped) { scrollToOffset(DoubleSize(scrollXOffset(), y), clamp); }
+    void scrollToOffset(const DoubleSize& scrollOffset, ScrollOffsetClamping = ScrollOffsetUnclamped, ScrollBehavior = ScrollBehaviorInstant);
+
+    void scrollToXOffset(double x, ScrollOffsetClamping clamp = ScrollOffsetUnclamped, ScrollBehavior scrollBehavior = ScrollBehaviorInstant)
+    {
+        scrollToOffset(DoubleSize(x, scrollYOffset()), clamp, scrollBehavior);
+    }
+
+    void scrollToYOffset(double y, ScrollOffsetClamping clamp = ScrollOffsetUnclamped, ScrollBehavior scrollBehavior = ScrollBehaviorInstant)
+    {
+        scrollToOffset(DoubleSize(scrollXOffset(), y), clamp, scrollBehavior);
+    }
 
     void updateAfterLayout();
     void updateAfterStyleChange(const RenderStyle*);
     void updateAfterOverflowRecalc();
 
     virtual bool updateAfterCompositingChange() override;
 
     bool hasScrollbar() const { return m_hBar || m_vBar; }
 
     RenderScrollbarPart* scrollCorner() const { return m_scrollCorner; }
@@ skipping 122 matching lines @@
     // Renderers to hold our custom scroll corner.
     RawPtrWillBePersistent<RenderScrollbarPart> m_scrollCorner;
 
     // Renderers to hold our custom resizer.
     RawPtrWillBePersistent<RenderScrollbarPart> m_resizer;
 };
 
 } // namespace blink
 
 #endif // RenderLayerScrollableArea_h