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

Source/core/page/scrolling/ScrollState.idl

Index: Source/core/page/scrolling/ScrollState.idl
diff --git a/Source/core/page/scrolling/ScrollState.idl b/Source/core/page/scrolling/ScrollState.idl
index 2c7dcbad41d11f554a60634f72413dff4575e598..228d973a682fe82b9b54840c35d2fc263f45f172 100644
--- a/Source/core/page/scrolling/ScrollState.idl
+++ b/Source/core/page/scrolling/ScrollState.idl
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// http://dev.w3.org/houdini/css-scroll-api/
+// https://docs.google.com/document/d/1VnvAqeWFG9JFZfgG5evBqrLGDZYRE5w6G5jEDORekPY
 
 [
     Constructor(optional double deltaX = 0,
@@ -28,5 +28,5 @@
     readonly attribute boolean shouldPropagate;
 
     [RaisesException] void consumeDelta(double x, double y);
-    // FIXME: implement distributeToScrollChainDescendent.
+    void distributeToScrollChainDescendant();
 };