Support registering and dispatching passive event listeners.

third_party/WebKit/Source/core/events/Event.cpp

Index: third_party/WebKit/Source/core/events/Event.cpp
diff --git a/third_party/WebKit/Source/core/events/Event.cpp b/third_party/WebKit/Source/core/events/Event.cpp
index 9f09da20a324bab98a8f138c413bd6dbb14a4328..1b2daab043a2a7a1fcdf81159dcaf9ef8ca4989c 100644
--- a/third_party/WebKit/Source/core/events/Event.cpp
+++ b/third_party/WebKit/Source/core/events/Event.cpp
@@ -54,6 +54,7 @@ Event::Event(const AtomicString& eventType, bool canBubbleArg, bool cancelableAr
     , m_defaultHandled(false)
     , m_cancelBubble(false)
     , m_isTrusted(false)
+    , m_handlingPassive(false)
     , m_eventPhase(0)
     , m_currentTarget(nullptr)
     , m_createTime(convertSecondsToDOMTimeStamp(currentTime()))
@@ -179,6 +180,19 @@ 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)