Enumerate the return value of dispatchEvent so it is clear.

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

Index: third_party/WebKit/Source/core/events/EventTarget.h
diff --git a/third_party/WebKit/Source/core/events/EventTarget.h b/third_party/WebKit/Source/core/events/EventTarget.h
index 5f56ecb04adcf376f578f59ca61a2f76aede39e3..15cf5fa9415a6bf30b56e0c4cfdb1037497a943c 100644
--- a/third_party/WebKit/Source/core/events/EventTarget.h
+++ b/third_party/WebKit/Source/core/events/EventTarget.h
@@ -114,6 +114,17 @@ public:
 class CORE_EXPORT EventTarget : public NoBaseWillBeGarbageCollectedFinalized<EventTarget>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
+    enum class DispatchEventResult {

[tkent, 2016/02/22 01:40:22]

nit: You may move this out from EventTarget for code simplicity.

[dtapuska, 2016/02/23 19:14:40]

Done.

+        // Event was not consumed by application or system.
+        NotHandled,

[philipj_slow, 2016/02/22 07:30:18]

In order to bring this closer to the
https://dom.spec.whatwg.org/#concept-event-dispatch model, can you put the two
cases corresponding to the true/false return values of dispatchEvent at the top,
and give the other two long and scary names as well as comments that they should
not be used?

Maybe NotCanceled, Canceled(ByEventHandler), CanceledByDefaultEventHandler and
CanceledBeforeDispatch, if that's accurate?

[Rick Byers, 2016/02/22 15:16:14]

+1.  This is the place to describe how we want the usage of these to evolve over
time to better match the spec.

[dtapuska, 2016/02/23 19:14:40]

Done.

[dtapuska, 2016/02/23 19:14:40]

Done.

+        // Event was consumed but suppressed before dispatched to application.
+        HandledSuppressed,
+        // Event was consumed by application itself; ie. a script handler calling preventDefault.
+        HandledApplication,
+        // Event was consumed by the system; ie. executing the default action.
+        HandledSystem,
+    };
+
     virtual ~EventTarget();
 
 #if !ENABLE(OILPAN)
@@ -138,7 +149,7 @@ public:
     bool removeEventListener(const AtomicString& eventType, PassRefPtrWillBeRawPtr<EventListener>, EventListenerOptions&);
     virtual void removeAllEventListeners();
 
-    bool dispatchEvent(PassRefPtrWillBeRawPtr<Event>);
+    EventTarget::DispatchEventResult dispatchEvent(PassRefPtrWillBeRawPtr<Event>);
 
     // dispatchEventForBindings is intended to only be called from
     // javascript originated calls. This method will validate and may adjust
@@ -156,7 +167,7 @@ public:
     EventListenerVector* getEventListeners(const AtomicString& eventType);
     Vector<AtomicString> eventTypes();
 
-    bool fireEventListeners(Event*);
+    EventTarget::DispatchEventResult fireEventListeners(Event*);
 
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 
@@ -167,7 +178,7 @@ protected:
 
     virtual bool addEventListenerInternal(const AtomicString& eventType, PassRefPtrWillBeRawPtr<EventListener>, const EventListenerOptions&);
     virtual bool removeEventListenerInternal(const AtomicString& eventType, PassRefPtrWillBeRawPtr<EventListener>, const EventListenerOptions&);
-    virtual bool dispatchEventInternal(PassRefPtrWillBeRawPtr<Event>);
+    virtual EventTarget::DispatchEventResult dispatchEventInternal(PassRefPtrWillBeRawPtr<Event>);
 
     // Subclasses should likely not override these themselves; instead, they should subclass EventTargetWithInlineData.
     virtual EventTargetData* eventTargetData() = 0;