Add EventHandlerRegistry

Source/core/page/scrolling/ScrollingCoordinator.h

Index: Source/core/page/scrolling/ScrollingCoordinator.h
diff --git a/Source/core/page/scrolling/ScrollingCoordinator.h b/Source/core/page/scrolling/ScrollingCoordinator.h
index 2423b1dfbccbe68cec3f2623172d939961e6770e..0614825ae11c59d045acf7f48c263f25e9fe793f 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.h
+++ b/Source/core/page/scrolling/ScrollingCoordinator.h
@@ -68,9 +68,11 @@ public:
 
     bool needsToUpdateAfterCompositingChange() const { return m_scrollGestureRegionIsDirty || m_touchEventTargetRectsAreDirty || frameViewIsDirty(); }
 
-    // Should be called whenever a wheel event handler is added or removed in the
-    // frame view's underlying document.
-    void frameViewWheelEventHandlerCountChanged(FrameView*);
+    // Should be called whenever the presence of wheel event handlers in the page changes.
+    void haveWheelEventHandlersChangedForPage();
+
+    // Should be called whenever the presence of scroll event handlers in the page changes.
+    void haveScrollEventHandlersChangedForPage();
 
     // Should be called whenever the slow repaint objects counter changes between zero and one.
     void frameViewHasSlowRepaintObjectsDidChange(FrameView*);
@@ -124,7 +126,6 @@ protected:
 
     bool isForMainFrame(ScrollableArea*) const;
 
-    unsigned computeCurrentWheelEventHandlerCount();
     GraphicsLayer* scrollLayerForFrameView(FrameView*);
     GraphicsLayer* counterScrollingLayerForFrameView(FrameView*);
 
@@ -136,7 +137,8 @@ protected:
     bool m_shouldScrollOnMainThreadDirty;
 
 private:
-    void recomputeWheelEventHandlerCountForFrameView(FrameView*);
+    void updateHaveWheelEventHandlers();
+    void updateHaveScrollEventHandlers();
     void setShouldUpdateScrollLayerPositionOnMainThread(MainThreadScrollingReasons);
 
     bool hasVisibleSlowRepaintViewportConstrainedObjects(FrameView*) const;
@@ -145,7 +147,6 @@ private:
     void setShouldHandleScrollGestureOnMainThreadRegion(const Region&);
     void setTouchEventTargetRects(const LayerHitTestRects&);
     void computeTouchEventTargetRects(LayerHitTestRects&);
-    void setWheelEventHandlerCount(unsigned);
 
     blink::WebScrollbarLayer* addWebScrollbarLayer(ScrollableArea*, ScrollbarOrientation, PassOwnPtr<blink::WebScrollbarLayer>);
     blink::WebScrollbarLayer* getWebScrollbarLayer(ScrollableArea*, ScrollbarOrientation);