Expose scroll customization for touch to JS (behind REF).

Source/core/dom/Element.h

Index: Source/core/dom/Element.h
diff --git a/Source/core/dom/Element.h b/Source/core/dom/Element.h
index fce9b0f4517892dc8e03737d1bf5166fc5d1e390..a097fdebd3287180b02970ed5fe9fa93e3938c52 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -62,6 +62,7 @@ class MutableStylePropertySet;
 class PropertySetCSSStyleDeclaration;
 class PseudoElement;
 class ScrollState;
+class ScrollStateCallback;
 class ScrollToOptions;
 class ShadowRoot;
 class ShadowRootInit;
@@ -84,6 +85,12 @@ enum ElementFlags {
     NumberOfElementFlags = 6, // Required size of bitfield used to store the flags.
 };
 
+enum NativeScrollBehavior {
+    DisableNativeScroll,
+    PerformBeforeNativeScroll,
+    PerformAfterNativeScroll,
+};
+
 typedef WillBeHeapVector<RefPtrWillBeMember<Attr>> AttrNodeList;
 
 class CORE_EXPORT Element : public ContainerNode {
@@ -170,9 +177,6 @@ public:
     void scrollIntoView(bool alignToTop = true);
     void scrollIntoViewIfNeeded(bool centerIfNeeded = true);
 
-    void distributeScroll(ScrollState&);
-    void applyScroll(ScrollState&);
-
     int offsetLeft();
     int offsetTop();
     int offsetWidth();
@@ -370,6 +374,15 @@ public:
     virtual void focus(bool restorePreviousSelection = true, WebFocusType = WebFocusTypeNone);
     virtual void updateFocusAppearance(bool restorePreviousSelection);
     virtual void blur();
+
+    void setDistributeScroll(ScrollStateCallback*, String nativeScrollBehavior);
+    void nativeDistributeScroll(ScrollState&);
+    void setApplyScroll(ScrollStateCallback*, String nativeScrollBehavior);
+    void nativeApplyScroll(ScrollState&);
+
+    void callDistributeScroll(ScrollState&);
+    void callApplyScroll(ScrollState&);
+
     // Whether this element can receive focus at all. Most elements are not
     // focusable but some elements, such as form controls and links, are. Unlike
     // layoutObjectIsFocusable(), this method may be called when layout is not up to