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

Source/core/testing/Internals.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 293 matching lines @@
     [TypeChecking=Interface] boolean isInCanvasFontCache(Document document, DOMString fontString);
     [TypeChecking=Interface] unsigned long canvasFontCacheMaxFonts();
 
     [TypeChecking=Interface] ClientRect boundsInViewportSpace(Element element);
 
     [RaisesException, TypeChecking=Interface] void forcePluginPlaceholder(HTMLElement plugin, DocumentFragment fragment);
     [RaisesException, TypeChecking=Interface] void forcePluginPlaceholder(HTMLElement plugin, PluginPlaceholderOptions options);
 
     DictionaryTest dictionaryTest();
     UnionTypesTest unionTypesTest();
-
+    [RaisesException, TypeChecking=Interface] void setScrollChain(ScrollState scrollState, Element[] elements);
     void forceBlinkGCWithoutV8GC();
 
     DOMString selectedHTMLForClipboard();
     DOMString selectedTextForClipboard();
 
     void setVisualViewportOffset(long x, long y);
 
     boolean isUseCounted(Document document, long useCounterId);
 
     iterable<long>;
 
     [Unscopeable] readonly attribute DOMString unscopeableAttribute;
     [Unscopeable] DOMString unscopeableMethod();
 
     ClientRectList focusRingRects(Element element);
     void setCapsLockState(boolean enabled);
 };