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

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 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 28 matching lines @@
 #include "core/html/HTMLVideoElement.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/layout/LayoutEmbeddedObject.h"
 #include "core/layout/LayoutHTMLCanvas.h"
 #include "core/layout/LayoutImage.h"
 #include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutVideo.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/api/LayoutAPIShim.h"
+#include "core/layout/api/LayoutPartItem.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/Page.h"
 #include "core/page/scrolling/ScrollingCoordinator.h"
 #include "core/paint/ObjectPaintInvalidator.h"
 #include "core/paint/PaintInfo.h"
 #include "core/paint/PaintLayerPainter.h"
 #include "core/paint/PaintLayerStackingNodeIterator.h"
 #include "core/paint/PaintTiming.h"
 #include "core/paint/ScrollableAreaPainter.h"
@@ skipping 2645 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink