Add EventHandlerRegistry

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
new file mode 100644
index 0000000000000000000000000000000000000000..dde20641c428ccdc74705796c5dd65ab488f28c9
--- /dev/null
+++ b/Source/core/dom/EventHandlerRegistry.h
@@ -0,0 +1,94 @@
+// 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/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
+// the DOM (e.g., WebViewImpl).
+class EventHandlerRegistry FINAL : public DocumentSupplement {
+public:
+    virtual ~EventHandlerRegistry();
+
+    // Supported event handler classes. Note that each one may correspond to
+    // multiple event types.
+    enum EventHandlerClass {
+        ScrollEvent,
+        EventHandlerClassCount, // Must be the last entry.
+    };
+
+    static const char* supplementName();
+    static EventHandlerRegistry* from(Document&);
+
+    // Returns true if the host Document or any child documents have any
+    // registered event handlers of the class.
+    bool hasEventHandlers(EventHandlerClass) const;
+
+    // Returns a set of EventTargets which have registered handlers of the
+    // given class. Only contains targets directly in this document; all
+    // handlers in a child Document are collapsed to a single respective
+    // Document instance in the set.
+    const EventTargetSet* eventHandlerTargets(EventHandlerClass) const;
+
+    // Registration and management of event handlers attached to EventTargets.
+    void didAddEventHandler(EventTarget&, const AtomicString& eventType);
+    void didAddEventHandler(EventTarget&, EventHandlerClass);
+    void didRemoveEventHandler(EventTarget&, const AtomicString& eventType);
+    void didRemoveEventHandler(EventTarget&, EventHandlerClass);
+    void didMoveFromOtherDocument(EventTarget&, Document& oldDocument);
+    void didRemoveAllEventHandlers(EventTarget&);
+
+    virtual void trace(Visitor*) OVERRIDE { }
+
+private:
+    explicit EventHandlerRegistry(Document&);
+
+    enum ChangeOperation {
+        Add, // Add a new event handler.
+        Remove, // Remove an existing event handler.
+        RemoveAll // Remove any and all existing event handlers for a given target.
+    };
+
+    // Returns true if |eventType| belongs to a class this registry tracks.
+    static bool eventTypeToClass(const AtomicString& eventType, EventHandlerClass* result);
+
+    // Returns true if the operation actually added a new target or completely
+    // removed an existing one.
+    bool updateEventHandlerTargets(ChangeOperation, EventHandlerClass, EventTarget*);
+
+    // Called on the EventHandlerRegistry of the root Document to notify
+    // clients when we have added the first handler or removed the last one for
+    // 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*);
+
+    struct HandlerState {
+        HandlerState();
+        ~HandlerState();
+
+        OwnPtr<EventTargetSet> targets;
+    };
+
+    Document& m_document;
+    HandlerState m_eventHandlers[EventHandlerClassCount];
+};
+
+} // namespace WebCore
+
+#endif // EventHandlerRegistry_h