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

Source/core/page/scrolling/ScrollStateCallback.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ScrollStateCallback_h
+#define ScrollStateCallback_h
+
+#include "bindings/core/v8/ScrollStateCallbackToScriptValue.h"
+#include "core/dom/Element.h"
+#include "platform/heap/GarbageCollected.h"
+
+namespace blink {
+
+class ScrollState;
+
+class ScrollStateCallback : public GarbageCollectedFinalized<ScrollStateCallback> {
+public:
+    enum class CallbackType {
+        UNSET,
+        APPLY_SCROLL,
+        DISTRIBUTE_SCROLL,
+    };
+    ScrollStateCallback();
+    virtual ~ScrollStateCallback() {}
+    DEFINE_INLINE_VIRTUAL_TRACE() { visitor->trace(m_targetElement); }
+    virtual void handleEvent(ScrollState*) = 0;
+    void handleEventForElement(Element& targetElement, ScrollState*);
+    ScriptValue toScriptValue(ScriptState* scriptState) { return scrollStateCallbackToScriptValue(*this, scriptState); }
+    CallbackType callbackType() { return m_callbackType; }
+    void setCallbackType(CallbackType callbackType) { m_callbackType = callbackType; }
+
+protected:
+    // Used to pass the target element to handleEvent for native
+    // ScrollStateCallback implementations. Null except within the
+    // scope of |handleEventForElement|.
+    RefPtrWillBeMember<Element> m_targetElement;
+    CallbackType m_callbackType;
+};
+
+} // namespace blink
+
+#endif // ScrollStateCallback_h