Made PlatformWheelEvent a subclass of PlatformMouseEvent.

third_party/WebKit/Source/platform/PlatformMouseEvent.h

 /*
  * Copyright (C) 2004, 2005, 2006, 2009 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 28 matching lines @@
         // Real mouse input events or synthetic events that behave just like real events
         RealOrIndistinguishable,
         // Synthetic mouse events derived from touch input
         FromTouch,
         // Synthetic mouse events generated without a position, for example those generated
         // from keyboard input.
         Positionless,
     };
 
     PlatformMouseEvent()
-        : PlatformEvent(PlatformEvent::MouseMoved)
+        : PlatformMouseEvent(PlatformEvent::MouseMoved)
+    {
+    }
+
+    explicit PlatformMouseEvent(EventType type)
+        : PlatformEvent(type)
         , m_clickCount(0)
         , m_synthesized(RealOrIndistinguishable)
     {
     }
 
     PlatformMouseEvent(const IntPoint& position, const IntPoint& globalPosition, WebPointerProperties::Button button, EventType type, int clickCount, Modifiers modifiers, double timestamp)
         : PlatformEvent(type, modifiers, timestamp)
         , m_position(position)
         , m_globalPosition(globalPosition)
         , m_clickCount(clickCount)
@@ skipping 42 matching lines @@
     // For canvas hit region.
     // TODO(zino): This might make more sense to put in HitTestResults or
     // some other part of MouseEventWithHitTestResults, but for now it's
     // most convenient to stash it here. Please see: http://crbug.com/592947.
     String m_region;
 };
 
 } // namespace blink
 
 #endif // PlatformMouseEvent_h