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

Source/core/dom/Element.idl

 /*
  * Copyright (C) 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
+// See https://goo.gl/1ipTpP for details.
+enum NativeScrollBehavior { "disable-native-scroll", "perform-before-native-scroll", "perform-after-native-scroll" };
+
 // https://dom.spec.whatwg.org/#interface-element
 
 [
     TypeChecking=Interface,
 ] interface Element : Node {
     readonly attribute DOMString? namespaceURI;
     readonly attribute DOMString? prefix;
     readonly attribute DOMString localName;
     readonly attribute DOMString tagName;
 
@@ skipping 65 matching lines @@
     readonly attribute long clientWidth;
     readonly attribute long clientHeight;
     // http://dev.w3.org/csswg/cssom-view/#extensions-to-the-htmlelement-interface
     // FIXME: offset* should only be on HTMLElement.
     [MeasureAs=ElementOffsetParent, PerWorldBindings] readonly attribute Element? offsetParent;
     [MeasureAs=ElementOffsetTop] readonly attribute long offsetTop;
     [MeasureAs=ElementOffsetLeft] readonly attribute long offsetLeft;
     [MeasureAs=ElementOffsetWidth] readonly attribute long offsetWidth;
     [MeasureAs=ElementOffsetHeight] readonly attribute long offsetHeight;
 
+    // Scroll Customization API. See crbug.com/410974 for details.
+    [RuntimeEnabled=ScrollCustomization] void setApplyScroll(ScrollStateCallback scrollStateCallback, NativeScrollBehavior nativeScrollBehavior);
+    [RuntimeEnabled=ScrollCustomization] void setDistributeScroll(ScrollStateCallback scrollStateCallback, NativeScrollBehavior nativeScrollBehavior);
+
     // Non-standard APIs
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=19962
     [RaisesException, CustomElementCallbacks, MeasureAs=InsertAdjacentElement] Element insertAdjacentElement(DOMString where, Element element);
     [RaisesException, MeasureAs=InsertAdjacentText] void insertAdjacentText(DOMString where, DOMString text);
     [MeasureAs=ElementScrollIntoViewIfNeeded] void scrollIntoViewIfNeeded(optional boolean centerIfNeeded);
     [RaisesException, ImplementedAs=matches, MeasureAs=ElementPrefixedMatchesSelector] boolean webkitMatchesSelector(DOMString selectors);
 
     // Experimental accessibility API
     [RuntimeEnabled=ComputedAccessibilityInfo] readonly attribute DOMString? computedRole;
     [RuntimeEnabled=ComputedAccessibilityInfo] readonly attribute DOMString? computedName;
@@ skipping 10 matching lines @@
     [RuntimeEnabled=Touch] attribute EventHandler ontouchcancel;
     [RuntimeEnabled=Touch] attribute EventHandler ontouchend;
     [RuntimeEnabled=Touch] attribute EventHandler ontouchmove;
     [RuntimeEnabled=Touch] attribute EventHandler ontouchstart;
     attribute EventHandler onwheel;
 };
 
 Element implements ParentNode;
 Element implements ChildNode;
 Element implements NonDocumentTypeChildNode;