Implement CSSOM Smooth Scroll API

public/platform/WebCompositorSupport.h

Index: public/platform/WebCompositorSupport.h
diff --git a/public/platform/WebCompositorSupport.h b/public/platform/WebCompositorSupport.h
index 9f33d321c7811316432129aef9ab30bde28e42ea..e2042860b3f85d4ab7c911fb3d33261092dfa8fe 100644
--- a/public/platform/WebCompositorSupport.h
+++ b/public/platform/WebCompositorSupport.h
@@ -27,7 +27,9 @@
 #define WebCompositorSupport_h
 
 #include "WebAnimation.h"
+#include "WebAnimationCurve.h"
 #include "WebCommon.h"
+#include "WebFloatPoint.h"
 #include "WebLayerTreeView.h"
 #include "WebScrollbar.h"
 #include "WebScrollbarThemePainter.h"
@@ -49,6 +51,7 @@ class WebNinePatchLayer;
 class WebLayer;
 class WebScrollbarLayer;
 class WebScrollbarThemeGeometry;
+class WebScrollOffsetAnimationCurve;
 class WebSolidColorLayer;
 class WebThread;
 class WebTransformAnimationCurve;
@@ -89,6 +92,8 @@ public:
 
     virtual WebFloatAnimationCurve* createFloatAnimationCurve() { return 0; }
 
+    virtual WebScrollOffsetAnimationCurve* createScrollOffsetAnimationCurve(WebFloatPoint targetValue, WebAnimationCurve::TimingFunctionType) { return 0; }
+
     virtual WebTransformAnimationCurve* createTransformAnimationCurve() { return 0; }
 
     virtual WebTransformOperations* createTransformOperations() { return 0; }