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

Source/core/testing/Internals.h

Index: Source/core/testing/Internals.h
diff --git a/Source/core/testing/Internals.h b/Source/core/testing/Internals.h
index 90772c3efa2f98c6ea7b26cf7721a07a3103f360..150748df6afac895f985d744ea9b1e17f56664eb 100644
--- a/Source/core/testing/Internals.h
+++ b/Source/core/testing/Internals.h
@@ -345,7 +345,9 @@ public:
     void forcePluginPlaceholder(HTMLElement* plugin, PassRefPtrWillBeRawPtr<DocumentFragment>, ExceptionState&);
     void forcePluginPlaceholder(HTMLElement* plugin, const PluginPlaceholderOptions&, ExceptionState&);
 
-    // Scheudle a forced Blink GC run (Oilpan) at the end of event loop.
+    void setScrollChain(ScrollState*, const WillBeHeapVector<RefPtrWillBeMember<Element>>& elements, ExceptionState&);
+
+    // Schedule a forced Blink GC run (Oilpan) at the end of event loop.
     // Note: This is designed to be only used from PerformanceTests/BlinkGC to explicitly measure only Blink GC time.
     //       Normal LayoutTests should use gc() instead as it would trigger both Blink GC and V8 GC.
     void forceBlinkGCWithoutV8GC();