Support registering and dispatching passive event listeners.

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 36 matching lines @@
 Event::Event(const AtomicString& eventType, bool canBubbleArg, bool cancelableArg, double platformTimeStamp)
     : m_type(eventType)
     , m_canBubble(canBubbleArg)
     , m_cancelable(cancelableArg)
     , m_propagationStopped(false)
     , m_immediatePropagationStopped(false)
     , m_defaultPrevented(false)
     , m_defaultHandled(false)
     , m_cancelBubble(false)
     , m_isTrusted(false)
+    , m_handlingPassive(false)
     , m_eventPhase(0)
     , m_currentTarget(nullptr)
     , m_createTime(convertSecondsToDOMTimeStamp(currentTime()))
     , m_platformTimeStamp(platformTimeStamp)
 {
 }
 
 Event::Event(const AtomicString& eventType, const EventInit& initializer)
     : Event(eventType, initializer.bubbles(), initializer.cancelable())
 {
@@ skipping 105 matching lines @@
 bool Event::isBeforeTextInsertedEvent() const
 {
     return false;
 }
 
 bool Event::isBeforeUnloadEvent() const
 {
     return false;
 }
 
+void Event::preventDefault()
+{
+    if (m_handlingPassive) {
+        const LocalDOMWindow* window = m_currentTarget ? m_currentTarget->toDOMWindow() : 0;
+        if (window)
+            window->printErrorMessage("Unable to preventDefault inside passive event listener invocation.");
+        return;
+    }
+
+    if (m_cancelable)
+        m_defaultPrevented = true;
+}
+
 void Event::setTarget(PassRefPtrWillBeRawPtr<EventTarget> target)
 {
     if (m_target == target)
         return;
 
     m_target = target;
     if (m_target)
         receivedTarget();
 }
 
@@ skipping 91 matching lines @@
 
 DEFINE_TRACE(Event)
 {
     visitor->trace(m_currentTarget);
     visitor->trace(m_target);
     visitor->trace(m_underlyingEvent);
     visitor->trace(m_eventPath);
 }
 
 } // namespace blink