Selectively disable rubber banding on mac.

Source/platform/scroll/ScrollAnimator.h

 /*
  * Copyright (c) 2010, Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 46 matching lines @@
     // destination and returns true.  Scrolling may be immediate or animated.
     // The base class implementation always scrolls immediately, never animates.
     virtual bool scroll(ScrollbarOrientation, ScrollGranularity, float step, float delta);
 
     virtual void scrollToOffsetWithoutAnimation(const FloatPoint&);
 
     ScrollableArea* scrollableArea() const { return m_scrollableArea; }
 
     virtual void setIsActive() { }
 
-    virtual bool handleWheelEvent(const PlatformWheelEvent&);
+    virtual bool handleWheelEvent(const PlatformWheelEvent&, bool canRubberbandLeft, bool canRubberbandRight);
 
 #if OS(MACOSX)
     virtual void handleWheelEventPhase(PlatformWheelEventPhase) { }
 #endif
 
     void setCurrentPosition(const FloatPoint&);
     FloatPoint currentPosition() const;
 
     virtual void cancelAnimations() { }
     virtual void serviceScrollAnimations() { }
@@ skipping 32 matching lines @@
     float m_currentPosX; // We avoid using a FloatPoint in order to reduce
     float m_currentPosY; // subclass code complexity.
 
 private:
     float clampScrollPosition(ScrollbarOrientation, float);
 };
 
 } // namespace WebCore
 
 #endif // ScrollAnimator_h