Make ViewportScrollCallback an interface and add child and root classes

third_party/WebKit/Source/core/page/scrolling/RootScrollerController.cpp

 // 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.
 
 #include "core/page/scrolling/RootScrollerController.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
@@ skipping 55 matching lines @@
         return false;
 
     if (!fillsViewport(element))
         return false;
 
     return true;
 }
 
 } // namespace
 
-ViewportScrollCallback* RootScrollerController::createViewportApplyScroll(
-    TopControls* topControls, OverscrollController* overscrollController)
-{
-    return new ViewportScrollCallback(topControls, overscrollController);
-}
-
 RootScrollerController::RootScrollerController(Document& document, ViewportScrollCallback* applyScrollCallback)
     : m_document(&document)
     , m_viewportApplyScroll(applyScrollCallback)
 {
 }
 
 DEFINE_TRACE(RootScrollerController)
 {
     visitor->trace(m_document);
     visitor->trace(m_viewportApplyScroll);
@@ skipping 64 matching lines @@
     m_viewportApplyScroll->setScroller(targetScroller);
 }
 
 Element* RootScrollerController::defaultEffectiveRootScroller()
 {
     DCHECK(m_document);
     return m_document->documentElement();
 }
 
 } // namespace blink