Articulate the cancel behavior in WebMouseWheelEvent.

third_party/WebKit/Source/platform/PlatformWheelEvent.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 48 matching lines @@
         : PlatformEvent(PlatformEvent::Wheel)
         , m_deltaX(0)
         , m_deltaY(0)
         , m_wheelTicksX(0)
         , m_wheelTicksY(0)
         , m_granularity(ScrollByPixelWheelEvent)
         , m_hasPreciseScrollingDeltas(false)
         , m_canScroll(true)
         , m_resendingPluginId(-1)
         , m_railsMode(RailsModeFree)
+        , m_dispatchType(Blocking)
 #if OS(MACOSX)
         , m_phase(PlatformWheelEventPhaseNone)
         , m_momentumPhase(PlatformWheelEventPhaseNone)
         , m_canRubberbandLeft(true)
         , m_canRubberbandRight(true)
 #endif
     {
     }
 
     const IntPoint& position() const { return m_position; } // PlatformWindow coordinates.
     const IntPoint& globalPosition() const { return m_globalPosition; } // Screen coordinates.
 
     float deltaX() const { return m_deltaX; }
     float deltaY() const { return m_deltaY; }
 
     float wheelTicksX() const { return m_wheelTicksX; }
     float wheelTicksY() const { return m_wheelTicksY; }
 
     PlatformWheelEventGranularity granularity() const { return m_granularity; }
 
     bool hasPreciseScrollingDeltas() const { return m_hasPreciseScrollingDeltas; }
     void setHasPreciseScrollingDeltas(bool b) { m_hasPreciseScrollingDeltas = b; }
     bool canScroll() const { return m_canScroll; }
     void setCanScroll(bool b) { m_canScroll = b; }
     int resendingPluginId() const { return m_resendingPluginId; }
     RailsMode getRailsMode() const { return m_railsMode; }
-
+    DispatchType dispatchType() const { return m_dispatchType; }
+    bool cancelable() const { return m_dispatchType == PlatformEvent::Blocking; }
 #if OS(MACOSX)
     PlatformWheelEventPhase phase() const { return m_phase; }
     PlatformWheelEventPhase momentumPhase() const { return m_momentumPhase; }
     bool canRubberbandLeft() const { return m_canRubberbandLeft; }
     bool canRubberbandRight() const { return m_canRubberbandRight; }
 #endif
 
 protected:
     IntPoint m_position;
     IntPoint m_globalPosition;
     float m_deltaX;
     float m_deltaY;
     float m_wheelTicksX;
     float m_wheelTicksY;
     PlatformWheelEventGranularity m_granularity;
     bool m_hasPreciseScrollingDeltas;
     bool m_canScroll;
     int m_resendingPluginId;
     RailsMode m_railsMode;
+    DispatchType m_dispatchType;
 #if OS(MACOSX)
     PlatformWheelEventPhase m_phase;
     PlatformWheelEventPhase m_momentumPhase;
     bool m_canRubberbandLeft;
     bool m_canRubberbandRight;
 #endif
 };
 
 } // namespace blink
 
 #endif // PlatformWheelEvent_h