Cleanup and refactor RootScrollerController.

third_party/WebKit/Source/core/page/scrolling/ChildViewportScrollCallback.h

-// Copyright 2016 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 ChildViewportScrollCallback_h
-#define ChildViewportScrollCallback_h
-
-#include "core/page/scrolling/ViewportScrollCallback.h"
-#include "platform/heap/Handle.h"
-
-namespace blink {
-
-class ScrollableArea;
-class ScrollState;
-
-// The ViewportScrollCallback used by non-root Frames, i.e. iframes. This is
-// essentially a no-op implementation that simply scrolls the frame since
-// iframes don't have any additional scrolling actions, unlike the root frame
-// which moves the top controls and provides overscroll glow.
-class ChildViewportScrollCallback : public ViewportScrollCallback {
-public:
-    static ChildViewportScrollCallback* create()
-    {
-        return new ChildViewportScrollCallback();
-    }
-
-    virtual ~ChildViewportScrollCallback();
-
-    void handleEvent(ScrollState*) override;
-    void setScroller(ScrollableArea*) override;
-
-    DECLARE_VIRTUAL_TRACE();
-
-private:
-    ChildViewportScrollCallback();
-
-    WeakMember<ScrollableArea> m_scroller;
-};
-
-} // namespace blink
-
-#endif // ChildViewportScrollCallback_h