Implement 'scroll-behavior' parsing

Source/platform/scroll/ScrollableArea.h

 /*
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 23 matching lines @@
 
 namespace WebCore {
 
 class FloatPoint;
 class GraphicsContext;
 class GraphicsLayer;
 class PlatformGestureEvent;
 class PlatformWheelEvent;
 class ScrollAnimator;
 
+enum ScrollBehavior {
+    ScrollBehaviorAuto,
+    ScrollBehaviorInstant,
+    ScrollBehaviorSmooth,
+};
+
 class PLATFORM_EXPORT ScrollableArea {
     WTF_MAKE_NONCOPYABLE(ScrollableArea);
 public:
     static int pixelsPerLineStep();
     static float minFractionToStepWhenPaging();
     static int maxOverlapBetweenPages();
 
     bool scroll(ScrollDirection, ScrollGranularity, float delta = 1);
     void scrollToOffsetWithoutAnimation(const FloatPoint&);
     void scrollToOffsetWithoutAnimation(ScrollbarOrientation, float offset);
@@ skipping 188 matching lines @@
     // vertical-lr / ltr            NO                      NO
     // vertical-lr / rtl            NO                      YES
     // vertical-rl / ltr            YES                     NO
     // vertical-rl / rtl            YES                     YES
     IntPoint m_scrollOrigin;
 };
 
 } // namespace WebCore
 
 #endif // ScrollableArea_h