Implement MouseEvent buttons attribute.

Source/core/events/WheelEvent.h

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Samsung Electronics. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 50 matching lines @@
     }
 
     static PassRefPtrWillBeRawPtr<WheelEvent> create(const AtomicString& type, const WheelEventInit& initializer)
     {
         return adoptRefWillBeNoop(new WheelEvent(type, initializer));
     }
 
     static PassRefPtrWillBeRawPtr<WheelEvent> create(const FloatPoint& wheelTicks,
         const FloatPoint& rawDelta, unsigned deltaMode, PassRefPtrWillBeRawPtr<AbstractView> view,
         const IntPoint& screenLocation, const IntPoint& pageLocation,
-        bool ctrlKey, bool altKey, bool shiftKey, bool metaKey)
+        bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, unsigned short buttons)
     {
         return adoptRefWillBeNoop(new WheelEvent(wheelTicks, rawDelta, deltaMode, view,
-        screenLocation, pageLocation, ctrlKey, altKey, shiftKey, metaKey));
+        screenLocation, pageLocation, ctrlKey, altKey, shiftKey, metaKey, buttons));
     }
 
     double deltaX() const { return m_deltaX; } // Positive when scrolling right.
     double deltaY() const { return m_deltaY; } // Positive when scrolling down.
     double deltaZ() const { return m_deltaZ; }
     int wheelDelta() const { return wheelDeltaY() ? wheelDeltaY() : wheelDeltaX(); } // Deprecated.
     int wheelDeltaX() const { return m_wheelDelta.x(); } // Deprecated, negative when scrolling right.
     int wheelDeltaY() const { return m_wheelDelta.y(); } // Deprecated, negative when scrolling down.
     unsigned deltaMode() const { return m_deltaMode; }
     float ticksX() const { return static_cast<float>(m_wheelDelta.x()) / TickMultiplier; }
     float ticksY() const { return static_cast<float>(m_wheelDelta.y()) / TickMultiplier; }
 
     virtual const AtomicString& interfaceName() const override;
     virtual bool isMouseEvent() const override;
     virtual bool isWheelEvent() const override;
 
     virtual void trace(Visitor*) override;
 
 private:
     WheelEvent();
     WheelEvent(const AtomicString&, const WheelEventInit&);
     WheelEvent(const FloatPoint& wheelTicks, const FloatPoint& rawDelta,
         unsigned, PassRefPtrWillBeRawPtr<AbstractView>, const IntPoint& screenLocation, const IntPoint& pageLocation,
-        bool ctrlKey, bool altKey, bool shiftKey, bool metaKey);
+        bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, unsigned short buttons);
 
     IntPoint m_wheelDelta;
     double m_deltaX;
     double m_deltaY;
     double m_deltaZ;
     unsigned m_deltaMode;
 };
 
 DEFINE_EVENT_TYPE_CASTS(WheelEvent);
 
 class WheelEventDispatchMediator final : public EventDispatchMediator {
 public:
     static PassRefPtrWillBeRawPtr<WheelEventDispatchMediator> create(const PlatformWheelEvent&, PassRefPtrWillBeRawPtr<AbstractView>);
 private:
     WheelEventDispatchMediator(const PlatformWheelEvent&, PassRefPtrWillBeRawPtr<AbstractView>);
     WheelEvent& event() const;
     virtual bool dispatchEvent(EventDispatcher&) const override;
 };
 
 } // namespace blink
 
 #endif // WheelEvent_h