Track scroll event handlers in nested documents

Source/core/dom/EventHandlerRegistry.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef EventHandlerRegistry_h
 #define EventHandlerRegistry_h
 
+#include "core/dom/ActiveDOMObject.h"
 #include "core/dom/DocumentSupplementable.h"
 #include "core/events/Event.h"
 #include "wtf/HashCountedSet.h"
 
 namespace WebCore {
 
 typedef HashCountedSet<EventTarget*> EventTargetSet;
 
 // Registry for keeping track of event handlers. Handlers can either be
 // associated with an EventTarget or be "external" handlers which live outside
@@ skipping 53 matching lines @@
     // a given event class. |hasActiveHandlers| can be used to distinguish
     // between the two cases.
     void notifyHasHandlersChanged(EventHandlerClass, bool hasActiveHandlers);
 
     // Record a change operation to a given event handler class and notify any
     // parent registry and other clients accordingly.
     void updateEventHandlerOfType(ChangeOperation, const AtomicString& eventType, EventTarget*);
 
     void updateEventHandlerInternal(ChangeOperation, EventHandlerClass, EventTarget*);
 
+    class DocumentObserver: public ActiveDOMObject {

[abarth-chromium, 2014/04/22 23:40:26]

I still don't understand why we're using ActiveDOMObject rather than
DocumentLifecycleObserver.  This class isn't a DOM object.

[Sami, 2014/04/23 10:02:35]

Sorry if that wasn't clear. The reason is that when the
DocumentLifecycleObserver::documentWasDetached() notification comes in, the
document no longer has an association with its previous parent, so it's too late
to unregister any handlers.

Originally I was going to add an earlier notification to the observer, but ended
up using ActiveDOMObject based on your suggestion here:
https://codereview.chromium.org/206603002/#msg19

+    public:
+        explicit DocumentObserver(Document&);
+        virtual ~DocumentObserver();
+
+        // Inherited from ActiveDOMObject
+        virtual void stop() OVERRIDE;
+    };
+
     struct HandlerState {
         HandlerState();
         ~HandlerState();
 
         OwnPtr<EventTargetSet> targets;
     };
 
     Document& m_document;
     HandlerState m_eventHandlers[EventHandlerClassCount];
+
+    DocumentObserver m_documentObserver;
 };
 
 } // namespace WebCore
 
 #endif // EventHandlerRegistry_h