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

Source/core/dom/Element.idl

Index: Source/core/dom/Element.idl
diff --git a/Source/core/dom/Element.idl b/Source/core/dom/Element.idl
index e5a1ff84f14e6354da5610a95b998721479ddb03..d469e8a07abdc6d3e50ac3c8b42b62358f7ebb49 100644
--- a/Source/core/dom/Element.idl
+++ b/Source/core/dom/Element.idl
@@ -20,6 +20,8 @@
 
 // https://dom.spec.whatwg.org/#interface-element
 
+callback ScrollStateCallback = void (ScrollState scrollState);
+
 [
     TypeChecking=Interface,
 ] interface Element : Node {
@@ -116,6 +118,10 @@
     void focus();
     void blur();
 
+    // Scroll Customization API. See crbug.com/410974 for details.
+    [RuntimeEnabled=ScrollCustomization] void applyScroll(ScrollState scrollState);
+    [RuntimeEnabled=ScrollCustomization] void distributeScroll(ScrollState scrollState);
+
     // Non-standard APIs
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=19962
     [RaisesException, CustomElementCallbacks, MeasureAs=InsertAdjacentElement] Element insertAdjacentElement(DOMString where, Element element);