Don't include LayoutObject-derived headers where not needed.

third_party/WebKit/Source/core/page/scrolling/RootScrollerUtil.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/RootScrollerUtil.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/frame/FrameView.h"
-#include "core/layout/LayoutBox.h"
-#include "core/layout/LayoutObject.h"
+#include "core/layout/LayoutBoxModelObject.h"
 #include "core/paint/PaintLayerScrollableArea.h"
 
 namespace blink {
 
 namespace RootScrollerUtil {
 
 ScrollableArea* scrollableAreaFor(const Element& element) {
   if (&element == element.document().documentElement()) {
     if (!element.document().view())
       return nullptr;
 
     // For a FrameView, we use the layoutViewport rather than the
     // getScrollableArea() since that could be the RootFrameViewport. The
     // rootScroller's ScrollableArea will be swapped in as the layout viewport
     // in RootFrameViewport so we need to ensure we get the layout viewport.
     return element.document().view()->layoutViewportScrollableArea();
   }
 
   if (!element.layoutObject() || !element.layoutObject()->isBox())
     return nullptr;
 
   return static_cast<PaintInvalidationCapableScrollableArea*>(
-      toLayoutBox(element.layoutObject())->getScrollableArea());
+      toLayoutBoxModelObject(element.layoutObject())->getScrollableArea());
 }
 
 }  // namespace RootScrollerUtil
 
 }  // namespace blink