Make ViewportScrollCallback an interface and add child and root classes

third_party/WebKit/Source/core/page/scrolling/RootScrollerController.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 RootScrollerController_h
 #define RootScrollerController_h
 
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class Document;
 class Element;
-class OverscrollController;
-class TopControls;
 class ViewportScrollCallback;
 
 // Manages the root scroller associated with a given document. The root scroller
 // causes top controls movement, overscroll effects and prevents chaining
 // scrolls up further in the DOM. It can be set from script using
 // document.setRootScroller.
 //
 // There are two notions of a root scroller in this class: m_rootScroller and
 // m_effectiveRootScroller. The former is the Element that was set as the root
 // scroller using document.setRootScroller. If the page didn't set a root
@@ skipping 15 matching lines @@
     // ViewportScrollCallback can be provided. If it is, RootScrollerController
     // will ensure that the effectiveRootScroller element always has this set as
     // the apply scroll callback.
     static RootScrollerController* create(
         Document& document,
         ViewportScrollCallback* applyScrollCallback)
     {
         return new RootScrollerController(document, applyScrollCallback);
     }
 
-    // Creates an apply scroll callback that handles viewport actions like
-    // TopControls movement and Overscroll. The TopControls and
-    // OverscrollController are given to the ViewportScrollCallback but are not
-    // owned or kept alive by it.
-    static ViewportScrollCallback* createViewportApplyScroll(
-        TopControls*, OverscrollController*);
-
     DECLARE_TRACE();
 
     // Sets the element that will be used as the root scroller. This can be
     // nullptr, in which case we'll use the default element (documentElement) as
     // the effective root scroller.
     void set(Element*);
 
     // Returns the element currently set as the root scroller from script. This
     // differs from the effective root scroller since the set Element may not
     // currently be a valid root scroller. e.g. If the page sets an Element
@@ skipping 33 matching lines @@
     WeakMember<Document> m_document;
     Member<ViewportScrollCallback> m_viewportApplyScroll;
 
     WeakMember<Element> m_rootScroller;
     WeakMember<Element> m_effectiveRootScroller;
 };
 
 } // namespace blink
 
 #endif // RootScrollerController_h