Implement MouseEvent buttons attribute.

Source/core/events/WheelEvent.cpp

 /*
  * 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, 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 44 matching lines @@
     , m_deltaY(initializer.deltaY ? initializer.deltaY : -initializer.wheelDeltaY)
     , m_deltaZ(initializer.deltaZ)
     , m_deltaMode(initializer.deltaMode)
 {
 }
 
 WheelEvent::WheelEvent(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)
     : MouseEvent(EventTypeNames::wheel, true, true, view, 0, screenLocation.x(), screenLocation.y(),
-        pageLocation.x(), pageLocation.y(), 0, 0, ctrlKey, altKey, shiftKey, metaKey, 0, nullptr,
-        nullptr, false, PlatformMouseEvent::RealOrIndistinguishable)
+        pageLocation.x(), pageLocation.y(), 0, 0, ctrlKey, altKey, shiftKey, metaKey, 0, 0,

[Rick Byers, 2014/11/14 19:48:09]

WheelEvent is a MouseEvent too, so I think you'll need to support and test the
buttons value on it too (although I'd be curious to hear whether FireFox and IE
set it properly for wheel).

If that's going to take some non-trivial work (eg. maybe chromium isn't setting
the modifiers on WebWheelEvent today), then feel free to add a FIXME here
referencing your bug# and worry about that in follow-up CLs.  We don't want to
leave the API partially implemented for long though, we can put it behind a
RuntimeEnabledFeature if it's likely to take more than a week or so.

[zino, 2014/11/18 14:19:35]

Done.

+        nullptr, nullptr, false, PlatformMouseEvent::RealOrIndistinguishable)
     , m_wheelDelta(wheelTicks.x() * TickMultiplier, wheelTicks.y() * TickMultiplier)
     , m_deltaX(-rawDelta.x())
     , m_deltaY(-rawDelta.y())
     , m_deltaZ(0)
     , m_deltaMode(deltaMode)
 {
 }
 
 const AtomicString& WheelEvent::interfaceName() const
 {
@@ skipping 40 matching lines @@
     return toWheelEvent(EventDispatchMediator::event());
 }
 
 bool WheelEventDispatchMediator::dispatchEvent(EventDispatcher* dispatcher) const
 {
     ASSERT(event());
     return EventDispatchMediator::dispatchEvent(dispatcher) && !event()->defaultHandled();
 }
 
 } // namespace blink