Scroll Customization Prototype (Not for review, WIP)

Source/core/page/EventHandler.h

Index: Source/core/page/EventHandler.h
diff --git a/Source/core/page/EventHandler.h b/Source/core/page/EventHandler.h
index f385904dd3bc3922faa9cb9aaa9c279ffcc1a074..f2b235ad3e80c612afe6bfa5a5aa47bfbde13971 100644
--- a/Source/core/page/EventHandler.h
+++ b/Source/core/page/EventHandler.h
@@ -74,6 +74,7 @@ class LayerScrollableArea;
 class LayoutObject;
 class ScrollableArea;
 class Scrollbar;
+class ScrollState;
 class TextEvent;
 class VisibleSelection;
 class WheelEvent;
@@ -246,7 +247,7 @@ private:
 
     // Scrolls the elements of the DOM tree. Returns true if a node was scrolled.
     // False if we reached the root and couldn't scroll anything.
-    // direction - The direction to scroll in. If this is a logicl direction, it will be
+    // direction - The direction to scroll in. If this is a logical direction, it will be
     //             converted to the physical direction based on a node's writing mode.
     // granularity - The units that the  scroll delta parameter is in.
     // startNode - The node to start bubbling the scroll from. If a node can't scroll,
@@ -257,6 +258,8 @@ private:
     // absolutePoint - For wheel scrolls - the location, in absolute coordinates, where the event occured.
     bool scroll(ScrollDirection, ScrollGranularity, Node* startNode = nullptr, Node** stopNode = nullptr, float delta = 1.0f, IntPoint absolutePoint = IntPoint());
 
+    bool customizedScroll(ScrollState*, Node* startNode = nullptr);
+
     TouchAction intersectTouchAction(const TouchAction, const TouchAction);
     TouchAction computeEffectiveTouchAction(const Node&);
 
@@ -396,6 +399,14 @@ private:
     Timer<EventHandler> m_activeIntervalTimer;
     double m_lastShowPressTimestamp;
     RefPtrWillBeMember<Element> m_lastDeferredTapElement;
+
+    // The following are only used when the ScrollCustomization
+    // runtime enabled feature is on.
+    // The last element to be scrolled, if a scroll is in progress.
+    RefPtrWillBeMember<Element> m_currentNativeScrollingElement;
+    WillBeHeapVector<RefPtrWillBeMember<Element>> m_currentScrollChain;
+    // True iff an element is currently being scrolled.
+    bool m_scrollLockedToElement;
 };
 
 } // namespace blink