InitEvent should not do anything if dispatch flag is set.

third_party/WebKit/Source/core/events/UIEvent.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 Apple Inc. 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
  * version 2 of the License, or (at your option) any later version.
@@ skipping 65 matching lines @@
 {
 }
 
 void UIEvent::initUIEvent(const AtomicString& typeArg, bool canBubbleArg, bool cancelableArg, AbstractView* viewArg, int detailArg)
 {
     initUIEventInternal(typeArg, canBubbleArg, cancelableArg, nullptr, viewArg, detailArg, nullptr);
 }
 
 void UIEvent::initUIEventInternal(const AtomicString& typeArg, bool canBubbleArg, bool cancelableArg, EventTarget* relatedTarget, AbstractView* viewArg, int detailArg, InputDeviceCapabilities* sourceCapabilitiesArg)
 {
-    if (dispatched())
+    if (isBeingDispatched())
         return;
 
     initEvent(typeArg, canBubbleArg, cancelableArg, relatedTarget);
 
     m_view = viewArg;
     m_detail = detailArg;
     m_sourceCapabilities = sourceCapabilitiesArg;
 }
 
 bool UIEvent::isUIEvent() const
@@ skipping 12 matching lines @@
 }
 
 DEFINE_TRACE(UIEvent)
 {
     visitor->trace(m_view);
     visitor->trace(m_sourceCapabilities);
     Event::trace(visitor);
 }
 
 } // namespace blink