Implement CSSOM Smooth Scroll API

Source/core/rendering/RenderBox.h

Index: Source/core/rendering/RenderBox.h
diff --git a/Source/core/rendering/RenderBox.h b/Source/core/rendering/RenderBox.h
index e9541e8d8f70320a55ef53c2960971071d82fa0f..757342cdeffb4dce3c8c78f819b42945a33054d4 100644
--- a/Source/core/rendering/RenderBox.h
+++ b/Source/core/rendering/RenderBox.h
@@ -27,6 +27,7 @@
 #include "core/rendering/RenderOverflow.h"
 #include "core/rendering/shapes/ShapeOutsideInfo.h"
 #include "platform/scroll/ScrollTypes.h"
+#include "platform/scroll/ScrollableArea.h"
 
 namespace WebCore {
 
@@ -276,8 +277,8 @@ public:
     virtual LayoutUnit scrollHeight() const;
     int pixelSnappedScrollWidth() const;
     int pixelSnappedScrollHeight() const;
-    virtual void setScrollLeft(LayoutUnit);
-    virtual void setScrollTop(LayoutUnit);
+    virtual void setScrollLeft(LayoutUnit, ScrollBehavior);
+    virtual void setScrollTop(LayoutUnit, ScrollBehavior);
 
     void scrollToOffset(const IntSize&);
     void scrollByRecursively(const IntSize& delta, ScrollOffsetClamping = ScrollOffsetUnclamped);