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 "core/dom/Element.h"
+#include "platform/heap/GarbageCollected.h"
+
+namespace blink {
+
+class ScrollState;
+
+class ScrollStateCallback : public RefCountedWillBeGarbageCollectedFinalized<ScrollStateCallback> {

[haraken, 2015/06/27 08:09:33]

I think we can just make Oilpan the default. WillBe is not needed. I think it
will simplify this CL.

  class ScrollStateCallback : public GarbageCollectedFinalized<class
ScrollStateCallback : public RefCountedWillBeGarbageCollectedFinalized> { ... };

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

Thanks, that definitely simplifies things.

+public:
+    enum class CallbackType {
+        UNSET,
+        APPLY_SCROLL,
+        DISTRIBUTE_SCROLL,
+    };
+    ScrollStateCallback();
+    virtual ~ScrollStateCallback()
+    {
+    }
+    DEFINE_INLINE_VIRTUAL_TRACE() {}
+    virtual void handleEvent(ScrollState*) = 0;
+    void handleEventForElement(Element& targetElement, ScrollState*);
+    ScriptValue toScriptValue(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|.
+    Element* m_targetElement;

[haraken, 2015/06/27 08:09:33]

This is a strong reference, so shall we use Member<Element>?

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

It can't be a Member<Element> in the non-oilpan case, so I'm using
RefPtrWillBeMember here.

Personally I think this is clearer as a raw ptr - this is only non-null within a
very limited scope.

+    CallbackType m_callbackType;
+};
+
+} // namespace blink
+
+#endif // ScrollStateCallback_h