Use scroll customization primitives for touch scrolling (behind REF).

Source/core/page/EventHandler.h

 /*
  * Copyright (C) 2006, 2007, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 56 matching lines @@
 class OptionalCursor;
 class PlatformGestureEvent;
 class PlatformKeyboardEvent;
 class PlatformTouchEvent;
 class PlatformWheelEvent;
 class Layer;
 class LayerScrollableArea;
 class LayoutObject;
 class ScrollableArea;
 class Scrollbar;
+class ScrollState;
 class TextEvent;
 class VisibleSelection;
 class WheelEvent;
 class Widget;
 
 enum AppendTrailingWhitespace { ShouldAppendTrailingWhitespace, DontAppendTrailingWhitespace };
 enum class DragInitiator;
 
 class EventHandler : public NoBaseWillBeGarbageCollectedFinalized<EventHandler> {
     WTF_MAKE_NONCOPYABLE(EventHandler);
@@ skipping 151 matching lines @@
 
     void fakeMouseMoveEventTimerFired(Timer<EventHandler>*);
     void cancelFakeMouseMoveEvent();
     bool isCursorVisible() const;
     void updateCursor();
 
     ScrollableArea* associatedScrollableArea(const Layer*) const;
 
     // 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,
     //             the scroll bubbles up to the containing block.
     // stopNode - On input, if provided and non-null, the node at which we should stop bubbling on input.
     //            On output, if provided and a node was scrolled stopNode will point to that node.
     // delta - The delta to scroll by, in the units of the granularity parameter. (e.g. pixels, lines, pages, etc.)
     // 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());
 
+    void customizedScroll(const Node& startNode, ScrollState&);
+
     TouchAction intersectTouchAction(const TouchAction, const TouchAction);
     TouchAction computeEffectiveTouchAction(const Node&);
 
     HitTestResult hitTestResultInFrame(LocalFrame*, const LayoutPoint&, HitTestRequest::HitTestRequestType hitType = HitTestRequest::ReadOnly | HitTestRequest::Active);
 
     void invalidateClick();
 
     void updateMouseEventTargetNode(Node*, const PlatformMouseEvent&, bool fireMouseOverOut);
 
     MouseEventWithHitTestResults prepareMouseEvent(const HitTestRequest&, const PlatformMouseEvent&);
@@ skipping 119 matching lines @@
     RefPtrWillBeMember<Node> m_previousGestureScrolledNode;
     RefPtrWillBeMember<Scrollbar> m_scrollbarHandlingScrollGesture;
 
     double m_maxMouseMovedDuration;
 
     bool m_longTapShouldInvokeContextMenu;
 
     Timer<EventHandler> m_activeIntervalTimer;
     double m_lastShowPressTimestamp;
     RefPtrWillBeMember<Element> m_lastDeferredTapElement;
+
+    // Only used with the ScrollCustomization runtime enabled feature.
+    WillBeHeapDeque<RefPtrWillBeMember<Element>> m_currentScrollChain;
+    // True iff some of the delta has been consumed for the current
+    // scroll sequence. Only used with ScrollCustomization.

[Rick Byers, 2015/03/11 02:22:19]

consumed within this frame, or by this frame any any child frames (which have
their own EventHandler instance)?

[tdresser, 2015/03/20 18:00:37]

Within this frame or any child frames. I've added a comment explaining how this
is used.

[Rick Byers, 2015/03/26 21:22:49]

Thanks, this is great.

+    bool m_deltaConsumedForScrollSequence;
 };
 
 } // namespace blink
 
 #endif // EventHandler_h