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..aa243dc8045bae20675ae5cea088d1f8e9dd2080 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.h
+++ b/Source/core/page/scrolling/ScrollingCoordinator.h
@@ -72,6 +72,10 @@ public:
     // frame view's underlying document.
     void frameViewWheelEventHandlerCountChanged(FrameView*);
 
+    // Should be called whenever a scroll event handler is added or removed in the
+    // frame view's underlying document.
+    void frameViewScrollEventHandlerCountChanged(FrameView*);
+
     // Should be called whenever the slow repaint objects counter changes between zero and one.
     void frameViewHasSlowRepaintObjectsDidChange(FrameView*);
 
@@ -125,6 +129,7 @@ protected:
     bool isForMainFrame(ScrollableArea*) const;
 
     unsigned computeCurrentWheelEventHandlerCount();
+    unsigned computeCurrentScrollEventHandlerCount();
     GraphicsLayer* scrollLayerForFrameView(FrameView*);
     GraphicsLayer* counterScrollingLayerForFrameView(FrameView*);
 
@@ -137,6 +142,7 @@ protected:
 
 private:
     void recomputeWheelEventHandlerCountForFrameView(FrameView*);
+    void recomputeScrollEventHandlerCountForFrameView(FrameView*);
     void setShouldUpdateScrollLayerPositionOnMainThread(MainThreadScrollingReasons);
 
     bool hasVisibleSlowRepaintViewportConstrainedObjects(FrameView*) const;
@@ -146,6 +152,7 @@ private:
     void setTouchEventTargetRects(const LayerHitTestRects&);
     void computeTouchEventTargetRects(LayerHitTestRects&);
     void setWheelEventHandlerCount(unsigned);
+    void setScrollEventHandlerCount(unsigned);
 
     blink::WebScrollbarLayer* addWebScrollbarLayer(ScrollableArea*, ScrollbarOrientation, PassOwnPtr<blink::WebScrollbarLayer>);
     blink::WebScrollbarLayer* getWebScrollbarLayer(ScrollableArea*, ScrollbarOrientation);