Track scroll event handlers in nested documents

Source/core/dom/EventHandlerRegistry.h

Index: Source/core/dom/EventHandlerRegistry.h
diff --git a/Source/core/dom/EventHandlerRegistry.h b/Source/core/dom/EventHandlerRegistry.h
index dde20641c428ccdc74705796c5dd65ab488f28c9..7e85204c9085e1e18d5744774f02cac943383567 100644
--- a/Source/core/dom/EventHandlerRegistry.h
+++ b/Source/core/dom/EventHandlerRegistry.h
@@ -5,6 +5,7 @@
 #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"
@@ -78,6 +79,15 @@ private:
 
     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();
@@ -87,6 +97,8 @@ private:
 
     Document& m_document;
     HandlerState m_eventHandlers[EventHandlerClassCount];
+
+    DocumentObserver m_documentObserver;
 };
 
 } // namespace WebCore