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 2d0574cfa815845e8441d21b7fbdeb810a129890..dd79478aaba27cbdac528896dc03039ced70fb94 100644
--- a/Source/core/dom/Element.idl
+++ b/Source/core/dom/Element.idl
@@ -18,6 +18,9 @@
  * Boston, MA 02110-1301, USA.
  */
 
+// http://dev.w3.org/houdini/css-scroll-api/

[Rick Byers, 2015/07/07 21:24:40]

Since there's nothing here yet, you should instead reference your bug or your
own API doc (something that describes the semantics of the API).

[tdresser, 2015/07/13 17:36:52]

Done.

+enum NativeScrollBehavior { "disable-native-scroll", "perform-before-native-scroll", "perform-after-native-scroll" };
+
 // https://dom.spec.whatwg.org/#interface-element
 
 [
@@ -103,6 +106,10 @@
     [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);