Migrate wheel events to EventHandlerRegistry

Source/core/frame/EventHandlerRegistry.h

Index: Source/core/frame/EventHandlerRegistry.h
diff --git a/Source/core/frame/EventHandlerRegistry.h b/Source/core/frame/EventHandlerRegistry.h
index 3a49d51f7cee791aba2af98de053441bb538f02d..6298be7d014d78b5ebaefe1a00008bcb2dce0675 100644
--- a/Source/core/frame/EventHandlerRegistry.h
+++ b/Source/core/frame/EventHandlerRegistry.h
@@ -25,6 +25,7 @@ public:
     // multiple event types.
     enum EventHandlerClass {
         ScrollEvent,
+        WheelEvent,
 #if ASSERT_ENABLED
         // Additional event categories for verifying handler tracking logic.
         EventsForTesting,
@@ -38,6 +39,10 @@ public:
     // Returns a set of EventTargets which have registered handlers of the given class.
     const EventTargetSet* eventHandlerTargets(EventHandlerClass) const;
 
+    // Returns the number of external event handlers for a given class.
+    // External handlers are not included in |eventHandlerTargets|.
+    unsigned externalEventHandlerCount(EventHandlerClass) const;
+
     // Registration and management of event handlers attached to EventTargets.
     void didAddEventHandler(EventTarget&, const AtomicString& eventType);
     void didAddEventHandler(EventTarget&, EventHandlerClass);
@@ -53,6 +58,10 @@ public:
     // to handlers that are no longer related to it.
     void documentDetached(Document&);
 
+    // Registration of event handlers attached to non-DOM objects.
+    void didAddExternalEventHandler(const AtomicString& eventType);
+    void didRemoveExternalEventHandler(const AtomicString& eventType);
+
     void trace(Visitor*);
     void clearWeakMembers(Visitor*);
 
@@ -80,6 +89,7 @@ private:
     // parent registry and other clients accordingly.
     void updateEventHandlerOfType(ChangeOperation, const AtomicString& eventType, EventTarget*);
 
+    void updateExternalHandlerCount(ChangeOperation, EventHandlerClass);
     void updateEventHandlerInternal(ChangeOperation, EventHandlerClass, EventTarget*);
 
     void updateAllEventHandlers(ChangeOperation, EventTarget&);
@@ -87,7 +97,17 @@ private:
     void checkConsistency() const;
 
     FrameHost& m_frameHost;
-    EventTargetSet m_targets[EventHandlerClassCount];
+
+    struct HandlerState {
+        HandlerState();
+        ~HandlerState();
+
+        EventTargetSet targets;
+        // External handlers are not included in |targets|.
+        unsigned externalHandlerCount;
+    };
+
+    HandlerState m_handlers[EventHandlerClassCount];
 };
 
 } // namespace WebCore