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

Source/core/dom/ElementRareData.cpp

 /*
  * Copyright (C) 2012 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 21 matching lines @@
 #include "core/dom/ElementRareData.h"
 
 #include "core/style/ComputedStyle.h"
 
 namespace blink {
 
 struct SameSizeAsElementRareData : NodeRareData {
     short indices[2];
     LayoutSize sizeForResizing;
     IntSize scrollOffset;
-    void* pointers[13];
+    void* pointers[15];

[haraken, 2015/06/27 08:09:32]

It's unfortunate that we increase sizeof(ElementRareData) for runtime enabled
features that are currently disabled.

[tdresser, 2015/06/29 20:59:33]

Can you suggest an alternative? You previously mentioned the option of using a
v8 hidden value, but that would require a bunch of logic for interacting with
the v8 types.

We'd need to:
- When receiving the ScrollStateCallback, convert it into a v8::Value.
- When calling the ScrollStateCallback, convert it from a v8::Value.
- Fetch the v8::Object for the current element whenever we get or set a scroll
customization method.

I can give this a shot, but it feels a little bit heavier than would be ideal.

 };
 
 CSSStyleDeclaration& ElementRareData::ensureInlineCSSStyleDeclaration(Element* ownerElement)
 {
     if (!m_cssomWrapper)
         m_cssomWrapper = adoptPtrWillBeNoop(new InlineCSSStyleDeclaration(ownerElement));
     return *m_cssomWrapper;
 }
 
 AttrNodeList& ElementRareData::ensureAttrNodeList()
@@ skipping 12 matching lines @@
 #if ENABLE(OILPAN)
     visitor->trace(m_attrNodeList);
 #endif
     visitor->trace(m_elementAnimations);
     visitor->trace(m_cssomWrapper);
     visitor->trace(m_customElementDefinition);
     visitor->trace(m_generatedBefore);
     visitor->trace(m_generatedAfter);
     visitor->trace(m_generatedFirstLetter);
     visitor->trace(m_backdrop);
+    visitor->trace(m_applyScroll);
+    visitor->trace(m_distributeScroll);
     NodeRareData::traceAfterDispatch(visitor);
 }
 
 static_assert(sizeof(ElementRareData) == sizeof(SameSizeAsElementRareData), "ElementRareData should stay small");
 
 } // namespace blink