Enumerate the return value of dispatchEvent so it is clear.

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

Index: third_party/WebKit/Source/core/events/EventTarget.cpp
diff --git a/third_party/WebKit/Source/core/events/EventTarget.cpp b/third_party/WebKit/Source/core/events/EventTarget.cpp
index 15bd846035344ffc91e74802d52da4c5e6adea18..faee4eae832d2ee12e2936df5d1e759781944d71 100644
--- a/third_party/WebKit/Source/core/events/EventTarget.cpp
+++ b/third_party/WebKit/Source/core/events/EventTarget.cpp
@@ -249,8 +249,9 @@ bool EventTarget::clearAttributeEventListener(const AtomicString& eventType)
     return removeEventListener(eventType, listener, false);
 }
 
-bool EventTarget::dispatchEventForBindings(PassRefPtrWillBeRawPtr<Event> event, ExceptionState& exceptionState)
+bool EventTarget::dispatchEventForBindings(PassRefPtrWillBeRawPtr<Event> dispatchEvent, ExceptionState& exceptionState)
 {
+    RefPtrWillBeRawPtr<Event> event = dispatchEvent;

[philipj_slow, 2016/02/25 15:23:46]

If this is to protect the event for its use in the return clause, it can be
reverted if that is changed.

[dtapuska, 2016/02/25 22:06:10]

Done.

     if (event->type().isEmpty()) {
         exceptionState.throwDOMException(InvalidStateError, "The event provided is uninitialized.");
         return false;
@@ -264,23 +265,28 @@ bool EventTarget::dispatchEventForBindings(PassRefPtrWillBeRawPtr<Event> event,
         return false;
 
     event->setTrusted(false);
-    return dispatchEventInternal(event);
+
+    // Return whether the event was cancelled or not to JS not that it
+    // might have actually been handled; so throw away the result of
+    // dispatchEventInternal.
+    dispatchEventInternal(event);
+    return !event->defaultPrevented();

[philipj_slow, 2016/02/25 15:23:46]

Will this not be equivalent to dispatchEventInternal(event) !=
DispatchEventResult::CanceledByEventHandler? It would be worrying if there were
any difference.

[dtapuska, 2016/02/25 22:06:10]

Done.

 }
 
-bool EventTarget::dispatchEvent(PassRefPtrWillBeRawPtr<Event> event)
+DispatchEventResult EventTarget::dispatchEvent(PassRefPtrWillBeRawPtr<Event> event)
 {
     event->setTrusted(true);
     return dispatchEventInternal(event);
 }
 
-bool EventTarget::dispatchEventInternal(PassRefPtrWillBeRawPtr<Event> event)
+DispatchEventResult EventTarget::dispatchEventInternal(PassRefPtrWillBeRawPtr<Event> event)
 {
     event->setTarget(this);
     event->setCurrentTarget(this);
     event->setEventPhase(Event::AT_TARGET);
-    bool defaultWasNotPrevented = fireEventListeners(event.get());
+    DispatchEventResult result = fireEventListeners(event.get());
     event->setEventPhase(0);
-    return defaultWasNotPrevented;
+    return result;
 }
 
 void EventTarget::uncaughtExceptionInEventHandler()
@@ -348,14 +354,14 @@ void EventTarget::countLegacyEvents(const AtomicString& legacyTypeName, EventLis
     }
 }
 
-bool EventTarget::fireEventListeners(Event* event)
+DispatchEventResult EventTarget::fireEventListeners(Event* event)
 {
     ASSERT(!EventDispatchForbiddenScope::isEventDispatchForbidden());
     ASSERT(event && !event->type().isEmpty());
 
     EventTargetData* d = eventTargetData();
     if (!d)
-        return true;
+        return DispatchEventResult::NotCanceled;
 
     EventListenerVector* legacyListenersVector = nullptr;
     AtomicString legacyTypeName = legacyType(event);
@@ -375,7 +381,7 @@ bool EventTarget::fireEventListeners(Event* event)
 
     Editor::countEvent(executionContext(), event);
     countLegacyEvents(legacyTypeName, listenersVector, legacyListenersVector);
-    return !event->defaultPrevented();
+    return event->eventResult();
 }
 
 void EventTarget::fireEventListeners(Event* event, EventTargetData* d, EventListenerVector& entry)