Don't include headers from the layout API from other headers needlessly.

third_party/WebKit/Source/core/layout/LayoutScrollbar.cpp

 /*
  * Copyright (C) 2008, 2009 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 13 matching lines @@
  */
 
 #include "core/layout/LayoutScrollbar.h"
 
 #include "core/css/PseudoStyleRequest.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutScrollbarPart.h"
 #include "core/layout/LayoutScrollbarTheme.h"
+#include "core/layout/LayoutView.h"
 #include "core/layout/api/LayoutAPIShim.h"
+#include "core/layout/api/LayoutPartItem.h"
 #include "core/paint/ObjectPaintInvalidator.h"
 #include "platform/graphics/GraphicsContext.h"
 
 namespace blink {
 
 Scrollbar* LayoutScrollbar::createCustomScrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, Node* ownerNode, LocalFrame* owningFrame)
 {
     return new LayoutScrollbar(scrollableArea, orientation, ownerNode, owningFrame);
 }
 
@@ skipping 315 matching lines @@
     return (orientation() == HorizontalScrollbar ? partLayoutObject->size().width() : partLayoutObject->size().height()).toInt();
 }
 
 void LayoutScrollbar::invalidateDisplayItemClientsOfScrollbarParts()
 {
     for (auto& part : m_parts)
         ObjectPaintInvalidator(*part.value).invalidateDisplayItemClientsIncludingNonCompositingDescendants(PaintInvalidationScroll);
 }
 
 } // namespace blink