blink: Cleanup class/struct forward declarations

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 PaintLayer;
 class PaintLayerScrollableArea;
-class ScrollableArea;
 
 // Manages the root scroller associated with a given document. The root
 // scroller causes browser 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
 // scroller this will be nullptr. The "effective" root scroller is the current
@@ skipping 75 matching lines @@
 
   // The element currently being used as the root scroller in this Document.
   // If the m_rootScroller is valid this will point to it. Otherwise, it'll
   // use a default Element.
   WeakMember<Element> m_effectiveRootScroller;
 };
 
 }  // namespace blink
 
 #endif  // RootScrollerController_h