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 15b035e41c1beb30438cd15e18b7205a5a81477a..1d092f2dc5ec9d33dfe466d3cd5bfa866c9fa5cc 100644
--- a/Source/core/dom/Element.idl
+++ b/Source/core/dom/Element.idl
@@ -116,6 +116,10 @@
     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);