InitEvent should not do anything if dispatch flag is set.

third_party/WebKit/Source/core/events/Event.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 96 matching lines @@
 {
 }
 
 void Event::initEvent(const AtomicString& eventTypeArg, bool canBubbleArg, bool cancelableArg)
 {
     initEvent(eventTypeArg, canBubbleArg, cancelableArg, nullptr);
 }
 
 void Event::initEvent(const AtomicString& eventTypeArg, bool canBubbleArg, bool cancelableArg, EventTarget* relatedTarget)
 {
-    if (dispatched())
+    if (isBeingDispatched())
         return;
 
     m_propagationStopped = false;
     m_immediatePropagationStopped = false;
     m_defaultPrevented = false;
     m_isTrusted = false;
 
     m_type = eventTypeArg;
     m_canBubble = canBubbleArg;
     m_cancelable = cancelableArg;
@@ skipping 229 matching lines @@
 
 DEFINE_TRACE(Event)
 {
     visitor->trace(m_currentTarget);
     visitor->trace(m_target);
     visitor->trace(m_underlyingEvent);
     visitor->trace(m_eventPath);
 }
 
 } // namespace blink