Implement CSSOM Smooth Scroll API

Source/core/rendering/RenderLayerScrollableArea.h

Index: Source/core/rendering/RenderLayerScrollableArea.h
diff --git a/Source/core/rendering/RenderLayerScrollableArea.h b/Source/core/rendering/RenderLayerScrollableArea.h
index 02ab6afc7f5f4c948bba9f9dd7a40ce802fb94d2..70d26f1b4865218cf5be35fa25b1903f673bedc2 100644
--- a/Source/core/rendering/RenderLayerScrollableArea.h
+++ b/Source/core/rendering/RenderLayerScrollableArea.h
@@ -110,6 +110,10 @@ public:
     virtual bool shouldPlaceVerticalScrollbarOnLeft() const OVERRIDE;
     virtual int pageStep(ScrollbarOrientation) const OVERRIDE;
 
+    virtual bool registerForAnimation() OVERRIDE;
+    virtual void deregisterForAnimation() OVERRIDE;
+    virtual bool scheduleAnimation() OVERRIDE;
+
     int scrollXOffset() const { return m_scrollOffset.width() + scrollOrigin().x(); }
     int scrollYOffset() const { return m_scrollOffset.height() + scrollOrigin().y(); }
 
@@ -118,9 +122,15 @@ public:
     // FIXME: We shouldn't allow access to m_overflowRect outside this class.
     LayoutRect overflowRect() const { return m_overflowRect; }
 
-    void scrollToOffset(const IntSize& scrollOffset, ScrollOffsetClamping = ScrollOffsetUnclamped);
-    void scrollToXOffset(int x, ScrollOffsetClamping clamp = ScrollOffsetUnclamped) { scrollToOffset(IntSize(x, scrollYOffset()), clamp); }
-    void scrollToYOffset(int y, ScrollOffsetClamping clamp = ScrollOffsetUnclamped) { scrollToOffset(IntSize(scrollXOffset(), y), clamp); }
+    void scrollToOffset(const IntSize& scrollOffset, ScrollOffsetClamping = ScrollOffsetUnclamped, ScrollBehavior = ScrollBehaviorInstant);
+    void scrollToXOffset(int x, ScrollOffsetClamping clamp = ScrollOffsetUnclamped, ScrollBehavior scrollBehavior = ScrollBehaviorInstant)
+    {
+        scrollToOffset(IntSize(x, scrollYOffset()), clamp, scrollBehavior);
+    }
+    void scrollToYOffset(int y, ScrollOffsetClamping clamp = ScrollOffsetUnclamped, ScrollBehavior scrollBehavior = ScrollBehaviorInstant)
+    {
+        scrollToOffset(IntSize(scrollXOffset(), y), clamp, scrollBehavior);
+    }
 
     void updateAfterLayout();
     void updateAfterStyleChange(const RenderStyle*);
@@ -226,6 +236,8 @@ private:
 
     void setForceNeedsCompositedScrolling(ForceNeedsCompositedScrollingMode);
 
+    virtual bool compositedScrollAnimationsEnabled() const OVERRIDE;
+
     RenderBox* m_box;
 
     // Keeps track of whether the layer is currently resizing, so events can cause resizing to start and stop.