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 18cce33bc7fdb7ccd6b19c907a8cdd2ac90f06b0..a98c7570f22024503f5b33caee45209f4abe1611 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 {
 
@@ -257,8 +258,8 @@ public:
     virtual int scrollTop() const;
     virtual int scrollWidth() const;
     virtual int scrollHeight() const;
-    virtual void setScrollLeft(int);
-    virtual void setScrollTop(int);
+    virtual void setScrollLeft(int, ScrollBehavior);
+    virtual void setScrollTop(int, ScrollBehavior);
 
     void scrollToOffset(const IntSize&);
     void scrollByRecursively(const IntSize& delta, ScrollOffsetClamping = ScrollOffsetUnclamped);